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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, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Restricted Class A Common Stock, Beginning Balance 1,614,907 1,484,175
Restricted Class A Common Stock, Granted 1,049,647 1,001,267
Restricted Class A Common Stock, Vested (948,407) (852,715)
Restricted Class A Common Stock, Forfeited (17,565) (17,820)
Restricted Class A Common Stock, Ending Balance 1,698,582 1,614,907
Weighted-Average Grant Date Fair Value Per Share, Beginning Balance $ 32.94 $ 30.61
Weighted-Average Grant Date Fair Value Per Share, Granted 34.69 33.93
Weighted-Average Grant Date Fair Value Per Share, Vested 32.08 30.10
Weighted-Average Grant Date Fair Value Per Share, Forfeited 31.55 30.44
Weighted-Average Grant Date Fair Value Per Share, Ending Balance $ 34.52 $ 32.94