Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 1.97	$ 1.77
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ 0	$ (0.01)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 34,472	$ 29,041
Calculation of Basic Earnings Per Share:
Net Income	$ 34,466	$ 28,930
Weighted shares outstanding (shares)	17,485,866	16,414,773
Basic Earnings Per Share (in dollars per share)	$ 1.97	$ 1.76
Reconciliation of Numerator:
Net Income	$ 34,466	$ 28,930
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	17,485,866	16,414,773
Effect of dilutive securities:
Share-based compensation (shares)	67,301	57,054
Adjusted denominator-Diluted (shares)	17,553,167	16,471,827
Income (Loss) from Continuing Operations, Per Diluted Share	$ 1.96	$ 1.77
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0	(0.01)
Diluted Earnings Per Share (in dollars per share)	$ 1.96	$ 1.76
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	$ (6)	$ (111)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	34,472	29,041
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	(6)	(111)
Net Income	$ 34,466	$ 28,930
Basic (shares)	17,485,866	16,414,773
Income (Loss) from Continuing Operations, Per Basic Share	$ 1.97	$ 1.77
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	0	(0.01)
Basic (in dollars per share)	$ 1.97	$ 1.76
Share-based compensation (shares)	67,301	57,054
Diluted (shares)	17,553,167	16,471,827
Income (Loss) from Continuing Operations, Per Diluted Share	$ 1.96	$ 1.77
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	$ 0	$ (0.01)
Retained Earnings [Member]
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 34,472	$ 29,041
Calculation of Basic Earnings Per Share:
Net Income	34,466	28,930
Reconciliation of Numerator:
Net Income	34,466	28,930
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	34,472	29,041
Net Income	$ 34,466	$ 28,930