Summarizes Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Options Outstanding, beginning balance, Shares	2,652,142	2,103,470	1,530,845
Granted, Shares	0	808,500	862,000
Exercised, Shares	(615,358)	(202,328)	(112,875)
Forfeited, Shares	(383,784)	(57,500)	(176,500)
Stock Options Outstanding, ending balance, Shares	1,653,000	2,652,142	2,103,470
Stock Options Exercisable, Shares	788,125	984,374	675,152
Stock Options Outstanding, beginning balance, Weighted-Average Exercise Price	$ 35.34	$ 32.72	$ 27.46
Granted, Weighted-Average Exercise Price		37.23	40.87
Exercised, Weighted-Average Exercise Price	24.01	13.62	13.24
Forfeited, Weighted-Average Exercise Price	39.59	42.54	39.32
Stock Options Outstanding, ending balance, Weighted-Average Exercise Price	38.53	35.34	32.72
Exercisable, Weighted-Average Exercise Price	$ 38.15	$ 29.84	$ 21.40
Stock Options Outstanding, Weighted-Average Remaining Contractual Term	4 years 3 months 10 days	4 years 9 months 3 days	4 years 10 months 9 days
Exercisable, Weighted-Average Remaining Contractual Term	3 years 8 months 15 days	3 years 5 months 8 days	3 years 5 months 12 days
Stock Options Outstanding, Aggregate Intrinsic Value	$ 3,610	$ 6,964	$ 12,265
Exercisable, Aggregate Intrinsic Value	$ 2,200	$ 6,534	$ 9,646