Summarizes Stock Appreciation Rights (SARs) Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
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
Exercisable, Ending Balance	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
Outstanding, Aggregate Intrinsic Value	$ 3,610	$ 6,964	$ 12,265
Exercisable, Aggregate Intrinsic Value	$ 2,200	$ 6,534	$ 9,646
Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options Outstanding, beginning balance, Shares	1,192,350	1,244,600	1,049,850
Granted, Shares		235,000	244,000
Exercised, Shares	(204,250)	(94,250)	(18,750)
Forfeited, Shares		(193,000)	(30,500)
Stock Options Outstanding, ending balance, Shares	988,100	1,192,350	1,244,600
Exercisable, Ending Balance	683,600	613,808	424,992
Stock Options Outstanding, beginning balance, Weighted-Average Exercise Price	$ 38.17	$ 36.11	$ 34.61
Granted, Weighted-Average Exercise Price		38.05	40.64
Exercised, Weighted-Average Exercise Price	26.35	22.21	24.28
Forfeited, Weighted-Average Exercise Price		32.53	28.23
Stock Options Outstanding, ending balance, Weighted-Average Exercise Price	40.61	38.17	36.11
Exercisable, Weighted Average Exercise Price	$ 41.21	$ 37.68	$ 34.49
Stock Options Outstanding, Weighted-Average Remaining Contractual Term	3 years 6 months 25 days	4 years 4 months 9 days	4 years 9 months 18 days
Exercisable, Weighted-Average Remaining Contractual Term	3 years 1 month 2 days	3 years 8 months 19 days	4 years 4 months 20 days
Outstanding, Aggregate Intrinsic Value	$ 2,064	$ 2,278	$ 3,511
Exercisable, Aggregate Intrinsic Value	$ 1,728	$ 1,904	$ 2,315