Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Additional Information (Details)

v3.7.0.1
Stock Based Compensation - Additional Information (Details)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2017
USD ($)
age
shares
Jun. 30, 2016
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Additional Employee Stock Plans Information        
Income tax expense (benefit) $ 7,608 $ 9,223 $ 4,914 $ 12,551
Performance Share Unit Awards | 2010 Plan        
Additional Employee Stock Plans Information        
Vesting period of awards     2 years  
Compensation expenses recognized 520 380 $ 671 506
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest 1,356   1,356  
Restricted Stock Unit Awards        
Additional Employee Stock Plans Information        
Compensation expenses recognized 238 $ 143 1,437 1,230
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest $ 727   727  
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     619 $ 528
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 (benefit)     $ 616