Quarterly report pursuant to Section 13 or 15(d)

Stock-based Compensation - Additional Information (Details)

v3.8.0.1
Stock-based Compensation - Additional Information (Details) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 9 Months Ended
May 31, 2017
Feb. 28, 2017
Sep. 30, 2017
Sep. 30, 2017
Sep. 30, 2016
Apr. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Stock-based compensation expense       $ 4,893 $ 6,200  
Stock Options [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of stock options granted to members of board of directors, executives, and non-executive employees       1,095,722    
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    
Stock Options [Member] | Non Executive Employee [Member] | Minimum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period       3 years    
Stock Options [Member] | Non Executive Employee [Member] | Maximum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period       4 years    
Stock Options [Member] | Directors [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period       1 year    
Performance Shares [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Stock-based compensation expense       $ 0    
Additional disclosures [Abstract]            
Options granted       412,500    
Grant date fair value     $ 700 $ 700    
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    
Restricted Stock Units (RSUs) [Member] | Non Executive Employee [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period       3 years    
Restricted Stock Units (RSUs) [Member] | Directors [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period       1 year    
2010 Plan [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of stock options granted to members of board of directors, executives, and non-executive employees 998,000 1,018,000        
Vesting period       3 years    
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]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Stock-based compensation expense     $ 500 $ 700    
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          
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%    
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