Annual report pursuant to Section 13 and 15(d)

Compensation and Other Benefit Plans - Additional Information (Details)

v3.8.0.1
Compensation and Other Benefit Plans - Additional Information (Details) - USD ($)
 1 Months Ended 12 Months Ended
Dec. 31, 2017
May 31, 2017
Feb. 28, 2017
May 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Apr. 30, 2017
Deferred savings plan [Abstract]                
Maximum annual contribution per employee (in hundredths)         50.00%      
Maximum annual contribution per employee         $ 18,000 $ 18,000 $ 18,000  
Maximum annual contribution per employee over 50 years old         $ 24,000 $ 24,000 $ 24,000  
Age requirement for participant to be eligible for a catch-up contribution, minimum         50 years 50 years 50 years  
Employer matching contribution percentage, maximum (in hundredths)         50.00%      
Deferred savings plan expense         $ 0 $ 500,000 $ 800,000  
Deferred savings plan expense paid in common shares (in hundredths)           100.00% 100.00%  
Number of shares of common stock to be issued upon exercise of options and RSUs outstanding (in shares) 1,641,492       1,641,492      
Additional disclosures [Abstract]                
Stock-based compensation expense         $ 7,301,000 $ 7,645,000 $ 9,727,000  
Non Executive Employee [Member] | Minimum [Member]                
Deferred savings plan [Abstract]                
Vesting period         3 years      
Non Executive Employee [Member] | Maximum [Member]                
Deferred savings plan [Abstract]                
Vesting period         4 years      
Directors [Member]                
Deferred savings plan [Abstract]                
Vesting period         1 year      
Executives [Member]                
Additional disclosures [Abstract]                
Additional options granted 130,000              
Stock Options [Member]                
Additional disclosures [Abstract]                
Minimum age required for employees to qualify for immediate vesting of RSUs         55 years      
Threshold years required for retirement age         70 years      
Options exercised, aggregate intrinsic value         $ 2,400,000   $ 400,000  
Stock options exercised         110,400 0    
Weighted-average grant-date fair value         $ 10.26 $ 4.90 $ 51.92  
Options outstanding, aggregate intrinsic value $ 34,300,000       $ 34,300,000      
Options outstanding, weighted average remaining contractual term         7 years 10 months 28 days      
Options exercisable, aggregate intrinsic value 18,500,000       $ 18,500,000      
Options exercisable, weighted average remaining contractual term         7 years 7 months 24 days      
Unrecognized compensation expense related to stock options $ 8,600,000       $ 8,600,000      
Weighted average period of unrecognized compensation expense expected to be recognized         2 years 2 months 12 days      
Number of stock options granted to members of board of directors, executives, and non-executive employees         1,387,820      
Stock options vested and expected to vest [Abstract]                
Options outstanding, number of shares (in shares) 1,622,065       1,622,065 568,292    
Options outstanding, weighted-average exercise price (in dollars per share) $ 24.54       $ 24.54 $ 77.70    
Stock option activity [Roll Forward]                
Exercisable at end of year (in shares) 849,279       849,279      
Performance Shares [Member]                
Additional disclosures [Abstract]                
Options granted         542,500      
Options vested         330,000      
Restricted Stock Units (RSUs) [Member]                
Additional disclosures [Abstract]                
Minimum age required for employees to qualify for immediate vesting of RSUs         55 years      
Threshold years required for retirement age         70 years      
Weighted average period of unrecognized compensation expense expected to be recognized         3 months 3 days      
Unrecognized compensation expense related to employee RSUs $ 88,000       $ 88,000      
Unvested RSU activity, weighted average grant date fair value [Roll Forward]                
Total grant-date fair value of RSUs, vested         $ 2,300,000 $ 5,300,000 $ 5,500,000  
Restricted Stock Units (RSUs) [Member] | Non Executive Employee [Member]                
Deferred savings plan [Abstract]                
Vesting period         3 years      
Restricted Stock Units (RSUs) [Member] | Directors [Member]                
Deferred savings plan [Abstract]                
Vesting period         1 year      
Common Stock [Member]                
Additional disclosures [Abstract]                
Stock options exercised         110,000      
2015 ESPP [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Percentage related to employees to purchase shares at the lower fair market value at offering period         85.00%      
Common stock reserved for future issuance (in shares) 15,000       15,000      
Percentage of compensation of eligible employees to purchase shares of entity common stock at discount through payroll deductions         10.00%      
Shares purchased (in shares)         5,314 7,070 6,029  
2015 ESPP [Member] | Common Stock [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in aggregate number of shares authorized for issuance   250,000            
Shares authorized for issuance   265,000           15,000
Increase in shares per person award limits   2,500            
2010 Plan [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in aggregate number of shares authorized for issuance       170,000        
Shares authorized for issuance       1,108,560        
Deferred savings plan [Abstract]                
Expiration period         ten years from the date of the grant or three to six months from the date of termination of employment (longer in case of death or certain retirements).      
Vesting period         3 years      
Additional disclosures [Abstract]                
Number of stock options granted to members of board of directors, executives, and non-executive employees   998,000 1,018,000          
2010 Plan [Member] | Options and Stock Appreciation Rights [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in shares per person award limits   2,000,000            
2010 Plan [Member] | Other Types of Stock Awards [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in shares per person award limits   2,000,000            
2010 Plan [Member] | Stock Options [Member]                
Additional disclosures [Abstract]                
Stock-based compensation expense         $ 1,800,000      
2010 Plan [Member] | Common Stock [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in aggregate number of shares authorized for issuance   1,470,502            
Shares authorized for issuance   2,579,062            
2010 Plan [Member] | Common Stock [Member] | Incentive Stock Options [Member]                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in aggregate number of shares authorized for issuance   2,004,087            
Shares authorized for issuance   2,579,062            
Long Term Incentive Plan [Member]                
Deferred savings plan [Abstract]                
Shares available for grant 412,314       412,314