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Stock-Based Incentive Plans - Movement in Outstanding Shares of Restricted Class A Common Stock and Weighted-Average Grant Date Fair Value Per Share (Detail) - Restricted Class A Common Stock [Member] - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Restricted Class A Common Stock, Beginning Balance 1,114,908 919,719
Restricted Class A Common Stock, Granted 872,294 679,958
Restricted Class A Common Stock, Vested (641,780) (456,626)
Restricted Class A Common Stock, Forfeited (35,427) (28,143)
Restricted Class A Common Stock, Ending Balance 1,309,995 1,114,908
Weighted-Average Grant Date Fair Value Per Share, Beginning Balance $ 27.64 $ 26.86
Weighted-Average Grant Date Fair Value Per Share, Granted 28.88 28.25
Weighted-Average Grant Date Fair Value Per Share, Vested 27.21 26.94
Weighted-Average Grant Date Fair Value Per Share, Forfeited 27.49 28.28
Weighted-Average Grant Date Fair Value Per Share, Ending Balance $ 28.68 $ 27.64