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], USD $)	9 Months Ended
	Sep. 30, 2014
Restricted Class A Common Stock [Member]
Schedule Of Share Based Compensation Restricted Stock Units Award Activity [Line Items]
Restricted Class A Common Stock, Beginning Balance	700,000
Restricted Class A Common Stock, Vested	(214,394)
Restricted Class A Common Stock, Ending Balance	485,606
Weighted-Average Grant Date Fair Value Per Share, Beginning Balance	$ 25.69
Weighted-Average Grant Date Fair Value Per Share, Vested	$ 25.56
Weighted-Average Grant Date Fair Value Per Share, Ending Balance	$ 25.75