Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 1.77	$ 1.76
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ (0.01)	$ (0.01)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 29,026,000	$ 28,814,000
Calculation of Basic Earnings Per Share:
Net Income	$ 28,930,000	$ 28,664,000
Weighted shares outstanding (shares)	16,414,773	16,384,927
Basic Earnings Per Share (in dollars per share)	$ 1.76	$ 1.75
Reconciliation of Numerator:
Net Income	$ 28,930,000	$ 28,664,000
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	16,414,773	16,384,927
Effect of dilutive securities:
Share-based compensation (shares)	57,054	47,925
Adjusted denominator-Diluted (shares)	16,471,827	16,432,852
Income (Loss) from Continuing Operations, Per Diluted Share	$ 1.77	$ 1.75
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	(0.01)	(0.01)
Diluted Earnings Per Share (in dollars per share)	$ 1.76	$ 1.74
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	$ (96,000)	$ (150,000)