Quarterly report pursuant to Section 13 or 15(d)

Employee Stock Plans - Additional Information (Details)

v3.8.0.1
Employee Stock Plans - Additional Information (Details)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
USD ($)
age
shares
Mar. 31, 2017
USD ($)
Additional Employee Stock Plans Information    
Income tax expense $ (1,262) $ (2,694)
Performance Share Unit Awards | 2010 Plan    
Additional Employee Stock Plans Information    
Vesting period of awards 2 years  
Compensation expenses recognized $ 491 151
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest 2,042  
Restricted Stock Unit Awards    
Additional Employee Stock Plans Information    
Compensation expenses recognized 929 1,198
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest $ 2,569  
Restricted Stock Unit Awards | Non-employee director    
Additional Employee Stock Plans Information    
Number of shares issued upon exercise of units other than options | shares 1  
Restricted Stock Unit Awards | Management    
Additional Employee Stock Plans Information    
Minimum age of employee, attaining which awards are continued to be vested upon retirement | age 65  
Minimum service period, upon serving which awards are continued to be vested upon retirement 10 years  
Minimum age of employee along with service period condition, attaining which awards are continued to be vested upon retirement | age 55  
Accelerated stock based compensation expense $ 742 619
Restricted Stock Unit Awards | Common Stock | Management    
Additional Employee Stock Plans Information    
Number of shares issued upon exercise of units other than options | shares 1  
Restricted Stock Unit Awards | 2010 Plan    
Additional Employee Stock Plans Information    
Maximum period following a termination of service in which the share-based award will be settled 2 months 15 days  
Accounting Standards Update 2016-09    
Additional Employee Stock Plans Information    
Income tax expense   $ 616