Share-Based Compensation - Certain Information Related to Stock Options and PSUs (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options Number of Options beginning balance	3,214
Stock Options Number of Options Granted	797
Stock Options Number of Options Exercised	(804)	(124)	(751)
Stock Options Number of Options ending balance	3,207	3,214
Stock Options Number of Options Exercisable	1,325
Stock Options Weighted Average Exercise Price per Share Outstanding beginning balance	$ 15.77
Stock Options Weighted Average Exercise Price per Share Granted	27.20
Stock Options Weighted Average Exercise Price per Share Exercised	6.95
Stock Options Weighted Average Exercise Price per Share Outstanding ending balance	20.82	$ 15.77
Stock Options Weighted Average Exercise Price per Share Exercisable	$ 18.62
Stock Options Aggregate Intrinsic Value Outstanding	$ 20,935
Stock Options Aggregate Intrinsic Value Exercisable	$ 11,570
Outstanding as of December 31, 2017	6 years 2 months 5 days
Exercisable Stock Options Weighted Average Remaining Term	4 years 5 months 20 days
Performance Share Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares beginning balance	173
Number of Shares Granted	147
Number of Shares Vested	(115)
Number of Shares ending balance	205	173
Weighted Average Grant Date Fair Value per Share beginning balance	$ 23.18
Weighted Average Grant Date Fair Value per Share Granted	27.20	$ 23.18
Weighted Average Grant Date Fair Value per Share Vested	23.18
Weighted Average Grant Date Fair Value per Share ending balance	$ 26.07	$ 23.18