Stock Based Compensation - Summary of Changes in Non Vested Shares of Restricted Stock Outstanding (Detail)	3 Months Ended
	Mar. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares, beginning balance | shares	3,913,634
Granted (unaudited), shares | shares	1,151,041
Vested shares | shares	(715,222)
Forfeited (unaudited), shares | shares	(109,987)
Non-vested shares, ending balance | shares	4,239,466
Non-vested, weighted average grant-date fair value, beginning of period | $ / shares	$ 37.12
Granted, weighted average grant-date fair value | $ / shares	46.21
Vested, weighted average grant-date fair value | $ / shares	58.48
Forfeited, weighted average grant-date fair value | $ / shares	33.71
Non-vested, weighted average grant-date fair value, end of period | $ / shares	$ 36.08