Annual report pursuant to Section 13 and 15(d)

Compensation and Other Benefit Plans - Additional Information (Details)

v3.3.1.900
Compensation and Other Benefit Plans - Additional Information (Details) - USD ($)
 1 Months Ended 12 Months Ended
May. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Deferred savings plan [Abstract]        
Maximum annual contribution per employee (in hundredths)   50.00%    
Maximum annual contribution per employee   $ 18,000 $ 17,500  
Maximum annual contribution per employee over 50 years old   $ 24,000 $ 23,000  
Age requirement for participant to be eligible for a catch-up contribution, minimum   50 years 50 years  
Employer matching contribution percentage, maximum (in hundredths)   50.00%    
Deferred savings plan expense   $ 800,000 $ 1,000,000 $ 900,000
Deferred savings plan expense paid in common shares (in hundredths)   100.00% 100.00% 100.00%
Number of shares of common stock to be issued upon exercise of options and RSUs outstanding (in shares)   10,148,543    
Directors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
Non Executive Employee        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   4 years    
Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   4 years    
Expiration period   ten years from the date of the grant or three months from the date of termination of employment (longer in case of death or certain retirements).    
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   $ 400,000 $ 2,900,000 $ 1,700,000
Options outstanding, aggregate intrinsic value   $ 13,000    
Options outstanding, weighted average remaining contractual term   6 years 3 months 18 days    
Options exercisable, aggregate intrinsic value   $ 10,000    
Options exercisable, weighted average remaining contractual term   5 years 8 months 12 days    
Unrecognized compensation expense related to stock options   $ 4,800,000    
Weighted average period of unrecognized compensation expense expected to be recognized   2 years 2 months 12 days    
Stock options vested and expected to vest [Abstract]        
Options vested and expected to vest, number of shares (in shares)   7,486,402    
Options vested and expected to vest, weighted-average exercise price (in dollars per share)   $ 6.37    
Stock option activity [Roll Forward]        
Exercisable at end of year (in shares)   5,604,615 4,908,925 4,814,926
Stock Options [Member] | Directors [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
Stock Options [Member] | Directors [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   3 years    
Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
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   1 year 6 months    
Unrecognized compensation expense related to employee RSUs   $ 4,900,000    
Unvested RSU activity, weighted average grant date fair value [Roll Forward]        
Total grant-date fair value of RSUs, vested   $ 5,500,000 $ 3,900,000 $ 1,600,000
Restricted Stock Units (RSUs) [Member] | Directors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
Restricted Stock Units (RSUs) [Member] | Employees [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   3 years    
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)   300,000    
Percentage of compensation of eligible employees to purchase shares of entity common stock at discount through payroll deductions   10.00%    
Employee Stock Purchase Plan [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   95.00%    
Shares authorized for issuance (in shares)   233,333    
Employee Stock Purchase Plan [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Employee compensation available for share purchases, maximum (in hundredths)   15.00%    
1998 and 2015 Employee Stock Purchase Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares purchased (in shares)   120,595 17,702 15,262
Net payroll deductions to acquire shares   $ 170,000 $ 74,000 $ 60,000
Long Term Incentive Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
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).    
Deferred savings plan [Abstract]        
Shares available for grant   3,935,778    
Long Term Incentive Plan [Member] | Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized for issuance (in shares) 18,771,206      
Deferred savings plan [Abstract]        
Additional shares authorized for issuance (in shares) 5,350,000      
Reducing shares from number of available shares (in shares) 1.18