Earnings Per Share - Calculations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Earnings Per Share Calculations Of Basic And Diluted Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 21,661	$ 9,280	$ 10,661	$ 29,041	$ 17,123	$ 6,251	$ 8,914	$ 28,811	$ 70,642	$ 61,100	$ 56,968
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax									$ 856	$ 4,053	$ (388)
Income (Loss) from Continuing Operations, Per Basic Share	$ 1.24	$ 0.56	$ 0.65	$ 1.77	$ 1.05	$ 0.38	$ 0.54	$ 1.76	$ 4.23	$ 3.73	$ 3.48
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ 0.04	$ 0	$ 0.02	$ (0.01)	$ 0.33	$ (0.04)	$ (0.03)	$ (0.01)	$ 0.05	$ 0.24	$ (0.02)
Calculation of Basic Earnings Per Share:
Net Income	$ 22,352	$ 9,261	$ 10,956	$ 28,930	$ 22,564	$ 5,621	$ 8,304	$ 28,663	$ 71,498	$ 65,153	$ 56,580
Weighted shares outstanding - Basic (in shares)									16,711,579	16,398,443	16,369,616
Basic Earnings Per Share (in usd per share)	$ 1.28	$ 0.56	$ 0.67	$ 1.76	$ 1.38	$ 0.34	$ 0.51	$ 1.75	$ 4.28	$ 3.97	$ 3.46
Calculation of Diluted Earnings Per Share:
Net Income	$ 22,352	$ 9,261	$ 10,956	$ 28,930	$ 22,564	$ 5,621	$ 8,304	$ 28,663	$ 71,498	$ 65,153	$ 56,580
Reconciliation of Denominator:
Weighted shares outstanding - Basic (in shares)									16,711,579	16,398,443	16,369,616
Share-based Compensation									59,156	50,043	50,254
Adjusted denominator — Diluted									16,770,735	16,448,486	16,419,870
Income (Loss) from Continuing Operations, Per Diluted Share	$ 1.24	$ 0.56	$ 0.64	$ 1.77	$ 1.04	$ 0.38	$ 0.54	$ 1.75	$ 4.21	$ 3.72	$ 3.47
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share	0.04	0	0.02	(0.01)	0.33	(0.04)	(0.04)	(0.01)	0.05	0.24	(0.02)
Diluted (in usd per share)	$ 1.28	$ 0.56	$ 0.66	$ 1.76	$ 1.37	$ 0.34	$ 0.50	$ 1.74	$ 4.26	$ 3.96	$ 3.45