Quarterly Financial Data - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disclosure Quarterly Financial Data Schedule Of Quarterly Financial Information [Abstract]
Revenues									$ 569,968	$ 488,198	$ 479,605
Operating Income									131,112	112,723	106,285
Net Income	$ 22,352	$ 9,261	$ 10,956	$ 28,930	$ 22,564	$ 5,621	$ 8,304	$ 28,663	83,466	71,498	65,153
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									83,467	70,642	61,100
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									(1)	686	(1,349)
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax									$ 0	$ 170	$ 5,402
Income (Loss) from Continuing Operations, Per Basic Share									$ 4.75	$ 4.23	$ 3.73
Earnings per share:
Basic (in usd per share)	$ 1.27	$ 0.56	$ 0.67	$ 1.76	$ 1.38	$ 0.34	$ 0.51	$ 1.75	4.75	4.28	3.97
Income (Loss) from Continuing Operations, Per Diluted Share									4.73	4.21	3.72
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share									0	0.05	0.24
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share									0	0.05	0.24
Diluted (in usd per share)	$ 1.26	$ 0.56	$ 0.66	$ 1.76	$ 1.37	$ 0.34	$ 0.50	$ 1.74	$ 4.73	$ 4.26	$ 3.96