Earnings Per Share - Calculations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Earnings Per Share Calculations Of Basic And Diluted Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 17,169	$ 6,246	$ 8,913	$ 28,814	$ 17,796	$ 6,090	$ 5,705	$ 27,271	$ 61,142	$ 56,862	$ 60,326
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax									$ 4,011	$ (282)	$ (2,202)
Income (Loss) from Continuing Operations, Per Basic Share	$ 1.05	$ 0.38	$ 0.54	$ 1.76	$ 1.09	$ 0.37	$ 0.35	$ 1.67	$ 3.73	$ 3.48	$ 3.69
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	$ 0.33	$ (0.04)	$ (0.03)	$ (0.01)	$ 0	$ (0.03)	$ 0.04	$ (0.03)	$ 0.24	$ (0.02)	$ (0.13)
Calculation of Basic Earnings Per Share:
Net Income	$ 22,562	$ 5,622	$ 8,304	$ 28,665	$ 17,801	$ 5,538	$ 6,385	$ 26,856	$ 65,153	$ 56,580	$ 58,124
Weighted shares outstanding - Basic (in shares)									16,398,443	16,369,616	16,336,789
Basic Earnings Per Share (in usd per share)	$ 1.38	$ 0.34	$ 0.51	$ 1.75	$ 1.09	$ 0.34	$ 0.39	$ 1.64	$ 3.97	$ 3.46	$ 3.56
Calculation of Diluted Earnings Per Share:
Net Income	$ 22,562	$ 5,622	$ 8,304	$ 28,665	$ 17,801	$ 5,538	$ 6,385	$ 26,856	$ 65,153	$ 56,580	$ 58,124
Reconciliation of Denominator:
Weighted shares outstanding - Basic (in shares)									16,398,443	16,369,616	16,336,789
Share-based Compensation									50,043	50,254	46,563
Adjusted denominator — Diluted									16,448,486	16,419,870	16,383,352
Income (Loss) from Continuing Operations, Per Diluted Share	$ 1.37	$ 0.38	$ 0.54	$ 1.75	$ 1.09	$ 0.37	$ 0.35	$ 1.66	$ 3.72	$ 3.47	$ 3.68
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share	1.04	(0.04)	(0.04)	(0.01)	0	(0.04)	0.04	(0.02)	0.24	(0.02)	(0.13)
Diluted (in usd per share)	$ 0.33	$ 0.34	$ 0.50	$ 1.74	$ 1.09	$ 0.33	$ 0.39	$ 1.64	$ 3.96	$ 3.45	$ 3.55