Stock-Based Compensation - Summary of Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding at beginning period - Options	1,257,730	1,216,700
Options granted	171,000	178,500
Options exercised	(76,650)	(107,470)
Options canceled, forfeited, or expired	(9,000)	(30,000)
Outstanding at ending period - Options	1,343,080	1,257,730
Exercisable at ending period - Options	710,330	644,730
Outstanding at beginning period - Wgtd. Avg. Exercise Price	$ 32.70	$ 28.48
Options granted - Wgtd. Avg. Exercise Price	48.89	56.87
Options exercised - Wgtd. Avg. Exercise Price	20.53	21.23
Options cancelled, forfeited, or expired - Wgtd. Avg. Exercise Price	58.26	46.42
Outstanding at ending period - Wgtd. Avg. Exercise Price	35.28	32.70
Exercisable at ending period - Wgtd. Avg. Exercise Price	$ 25.06	$ 23.09
Outstanding at ending period - Wgtd. Avg. Remaining Contractual Term, years	8 years 7 months 9 days	9 years 3 months 10 days
Exercisable at ending period - Wgtd. Avg. Remaining Contractual Term, years	6 years 11 months 8 days	7 years 1 month 6 days
Outstanding at ending period - Aggregate Intrinsic Value	$ 31,453	$ 37,408
Exercisable at ending period - Aggregate Intrinsic Value	$ 23,894	$ 25,370