Stock-Based Compensation Plans - Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	550,591	575,564	529,611
Number of Shares, Granted	13,900	82,474	168,217
Number of Shares, Canceled	(218)	(548)	(1,676)
Number of Shares, Exercised	(176,901)	(106,899)	(120,588)
Number of Shares, Ending Balance	387,372	550,591	575,564
Number of Shares, Exercisable	99,415
Weighted Average Exercise Price, Beginning Balance	$ 175.16	$ 132.93	$ 67.60
Weighted Average Exercise Price, Granted	368.10	279.57	261.19
Weighted Average Exercise Price, Canceled	307.52	198.67	142.69
Weighted Average Exercise Price, Exercised	84.07	28.24	24.66
Weighted Average Exercise Price, Ending Balance	223.60	$ 175.16	$ 132.93
Weighted Average Exercise Price, Exercisable	$ 137.78
Remaining Contractual Term, Outstanding at December 31, 2019	2 years 9 months 18 days
Remaining Contractual Term, Exercisable at December 31, 2020	1 year 8 months 12 days
Intrinsic Value, Exercised	$ 76,709
Intrinsic Value, Ending Balance	134,401
Intrinsic Value, Exercisable	$ 43,025