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Stock-Based Compensation - Deferred Stock Unit, Performance-Based Stock Unit and Restricted Stock Activity (Detail) - Deferred stock units, performance-based stock units and restricted stock [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Unvested, shares    
Unvested, Beginning Balance 670 455
Granted 413 286
Vested (89) (64)
Forfeited (61) (7)
Unvested, Ending Balance 933 670
Weighted Average Grant Date Fair Value    
Unvested, Beginning Balance $ 16.16 $ 17.09
Granted 13.27 15.02
Vested 16.46 17.42
Forfeited 17.08 18.76
Unvested ,Ending Balance $ 14.79 $ 16.16