Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 354,048	$ 365,424	$ 343,020	$ 335,208	$ 336,230	$ 345,558	$ 338,861	$ 326,738	$ 1,397,700	$ 1,347,387	$ 1,303,937
Gross profit	100,461	103,878	97,361	94,524	98,025	102,811	101,026	93,176	396,224	395,038	386,487
Income from continuing operations	18,285	18,763	9,885	9,106	14,609	15,907	16,076	7,974	56,039	54,566	50,876
Income from discontinued operations, net of tax	0	0	0	0	(401)	(967)	58,783	18,881	0	76,296	7,104
Net income	$ 18,285	$ 18,763	$ 9,885	$ 9,106	$ 14,208	$ 14,940	$ 74,859	$ 26,855	$ 56,039	$ 130,862	$ 57,980
Earnings per share – basic, continuing operations (in dollars per share)	$ 0.88	$ 0.90	$ 0.48	$ 0.42	$ 0.68	$ 0.70	$ 0.67	$ 0.33	$ 2.67	$ 2.35	$ 2.05
Earnings per share – diluted, continuing operations (in dollars per share)	0.86	0.89	0.47	0.42	0.66	0.68	0.66	0.32	2.62	2.29	2.02
Earnings per share – basic (in dollars per share)	0.88	0.90	0.48	0.42	0.66	0.66	3.13	1.10	2.67	5.64	2.34
Earnings per share – diluted (in dollars per share)	$ 0.86	$ 0.89	$ 0.47	$ 0.42	$ 0.64	$ 0.64	$ 3.06	$ 1.07	$ 2.62	$ 5.50	$ 2.30