v3.3.1.900
Stock-based Compensation - Summary of Activity for Non-voting Time-vested Restricted Stock Granted to Directors (Detail) - Non-Voting Time-Vested Restricted Stock Units [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Share unit, Beginning Balance 191,655  
Share unit, Granted 35,456  
Share unit, Forfeited (8,026)  
Share unit, Vested and released to participants (37,610)  
Share unit, Ending Balance 181,475 191,655
Weighted Average Grant Fair Value, Beginning Balance $ 38.56  
Weighted Average Grants Date Fair Value, Granted 30.17 $ 43.25
Weighted Average Grants Date Fair Value, Forfeited 22.81  
Weighted Average Grants Date Fair Value, Vested and released to participants (24.82)  
Weighted Average Grant Fair Value, Ending Balance $ 40.47 $ 38.56
Remaining Average Contractual Life, Ending 1 year 6 months 22 days 2 years 3 months 4 days
Aggregate Value, Beginning Balance $ 7,391  
Aggregate Value, Ending Balance $ 7,344 $ 7,391
Director [Member]    
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Share unit, Beginning Balance 4,488  
Share unit, Granted 4,317  
Share unit, Forfeited 0  
Share unit, Vested and released to participants 0  
Share unit, Ending Balance 8,805 4,488
Weighted Average Grant Fair Value, Beginning Balance $ 41.19  
Weighted Average Grants Date Fair Value, Granted 21.42  
Weighted Average Grants Date Fair Value, Forfeited 0  
Weighted Average Grants Date Fair Value, Vested and released to participants 0  
Weighted Average Grant Fair Value, Ending Balance $ 31.50 $ 41.19
Remaining Average Contractual Life, Ending 2 years 2 months 16 days 2 years 5 months 23 days
Aggregate Value, Beginning Balance $ 185  
Aggregate Value, Ending Balance $ 277 $ 185