Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.38	$ 0.37	$ 2.68	$ 2.39
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ (0.04)	$ (0.03)	$ (0.08)	$ (0.02)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 6,245,000	$ 6,090,000	$ 43,977,000	$ 39,118,000
Calculation of Basic Earnings Per Share:
Net Income	$ 5,621,000	$ 5,538,000	$ 42,589,000	$ 38,779,000
Weighted shares outstanding (shares)	16,403,776	16,378,545	16,396,646	16,366,608
Basic Earnings Per Share (in dollars per share)	$ 0.34	$ 0.34	$ 2.60	$ 2.37
Reconciliation of Numerator:
Net Income	$ 5,621,000	$ 5,538,000	$ 42,589,000	$ 38,779,000
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	16,403,776	16,378,545	16,396,646	16,366,608
Effect of dilutive securities:
Share-based compensation (shares)	50,091	49,894	47,585	49,647
Adjusted denominator-Diluted (shares)	16,453,867	16,428,439	16,444,231	16,416,255
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.38	$ 0.37	$ 2.67	$ 2.38
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	(0.04)	(0.03)	(0.08)	(0.02)
Diluted Earnings Per Share (in dollars per share)	$ 0.34	$ 0.34	$ 2.59	$ 2.36
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax	$ (624,000)	$ (552,000)	$ (1,388,000)	$ (339,000)