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Stock-based Compensation - Summary of Activity for Non-voting Time-vested Restricted Stock (Detail) - Non-Voting Time-Vested Restricted Stock Units [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Share unit, Beginning Balance 181,475  
Share unit, Granted 27,082  
Share unit, Forfeited (837)  
Share unit, Vested and released to participants (5,160)  
Share unit, Ending Balance 202,560 181,475
Weighted Average Grant Fair Value, Beginning Balance $ 40.47  
Weighted Average Grants Date Fair Value, Granted 20.07 $ 30.17
Weighted Average Grants Date Fair Value, Forfeited (36.45)  
Weighted Average Grants Date Fair Value, Vested and released to participants (34.45)  
Weighted Average Grant Fair Value, Ending Balance $ 37.91 $ 40.47
Remaining Average Contractual Life, Ending 1 year 3 months 1 year 6 months 22 days
Aggregate Value $ 7,679 $ 7,344