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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.79	$ 0.65	$ 2.76	$ 2.42
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ 0	$ 0.02	$ 0	$ 0.01
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 13,815	$ 10,661	$ 48,287	$ 39,702
Calculation of Basic Earnings Per Share:
Net Income	$ 13,813	$ 10,956	$ 48,279	$ 39,886
Weighted shares outstanding (shares)	17,546,346	16,448,490	17,516,273	16,431,724
Basic Earnings Per Share (in dollars per share)	$ 0.79	$ 0.67	$ 2.76	$ 2.43
Reconciliation of Numerator:
Net Income	$ 13,813	$ 10,956	$ 48,279	$ 39,886
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	17,546,346	16,448,490	17,516,273	16,431,724
Effect of dilutive securities:
Share-based compensation (shares)	70,150	55,113	68,733	56,083
Adjusted denominator-Diluted (shares)	17,616,496	16,503,603	17,585,006	16,487,807
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.78	$ 0.64	$ 2.75	$ 2.41
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0	0.02	0	0.01
Diluted Earnings Per Share (in dollars per share)	$ 0.78	$ 0.66	$ 2.75	$ 2.42
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	$ (2)	$ 295	$ (8)	$ 184
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	13,815	10,661	48,287	39,702
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	(2)	295	(8)	184
Net Income	$ 13,813	$ 10,956	$ 48,279	$ 39,886
Basic (shares)	17,546,346	16,448,490	17,516,273	16,431,724
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.79	$ 0.65	$ 2.76	$ 2.42
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	0	0.02	0	0.01
Basic (in dollars per share)	$ 0.79	$ 0.67	$ 2.76	$ 2.43
Share-based compensation (shares)	70,150	55,113	68,733	56,083
Diluted (shares)	17,616,496	16,503,603	17,585,006	16,487,807
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.78	$ 0.64	$ 2.75	$ 2.41
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0	0.02	0	0.01
Diluted (in dollars per share)	$ 0.78	$ 0.66	$ 2.75	$ 2.42
Retained Earnings [Member]
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 13,815	$ 10,661	$ 48,287	$ 39,702
Calculation of Basic Earnings Per Share:
Net Income	13,813	10,956	48,279	39,886
Reconciliation of Numerator:
Net Income	13,813	10,956	48,279	39,886
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	13,815	10,661	48,287	39,702
Net Income	$ 13,813	$ 10,956	$ 48,279	$ 39,886