Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.65	$ 0.55	$ 2.42	$ 2.31
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ 0.02	$ (0.04)	$ 0.01	$ (0.05)
Calculation of Basic Earnings Per Share:
Net Income	$ 10,956	$ 8,304	$ 39,886	$ 36,968
Weighted shares outstanding (shares)	16,448,490	16,401,028	16,431,724	16,393,022
Basic Earnings Per Share (in dollars per share)	$ 0.67	$ 0.51	$ 2.43	$ 2.26
Reconciliation of Numerator:
Net Income	$ 10,956	$ 8,304	$ 39,886	$ 36,968
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	16,448,490	16,401,028	16,431,724	16,393,022
Effect of dilutive securities:
Share-based compensation (shares)	55,113	44,715	56,083	46,311
Adjusted denominator-Diluted (shares)	16,503,603	16,445,743	16,487,807	16,439,333
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.64	$ 0.54	$ 2.41	$ 2.30
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0.02	(0.04)	0.01	(0.05)
Diluted Earnings Per Share (in dollars per share)	$ 0.66	$ 0.50	$ 2.42	$ 2.25
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	$ 295	$ (610)	$ 184	$ (757)