Quarterly Financial Data (Unaudited) - Summary of Unaudited Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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	$ 211,110	$ 238,389	$ 236,943	$ 277,455	$ 203,138	$ 239,790	$ 235,498	$ 269,998	$ 963,897	$ 948,424	$ 922,003
Operating expenses	211,748	204,760	209,016	199,827	200,706	209,146	198,148	215,496	825,351	823,496	790,283
Gross margin	(638)	33,629	27,927	77,628	2,432	30,644	37,350	54,502	138,546	124,928	131,720
Corporate general and administrative expenses	13,078	11,339	11,160	10,489	10,490	11,670	10,566	11,680	46,066	44,406	39,173
Operating income	(13,716)	22,290	16,767	67,139	(8,058)	18,974	26,784	42,822	92,480	80,522	92,547
Other (expense) income:
Interest expense	(816)	(974)	(2,074)	(1,119)	(1,256)	(1,521)	(1,587)	(1,401)	(4,983)	(5,765)	(6,645)
(Loss) gain on sale of operations, net	(587)	(74)	57	95	15	(145)	50	497	(509)	417	1,025
Other income, net	13,050	5,914	13,336	(15,800)	4,999	6,767	(3,311)	9,260	16,500	17,715	(7,087)
Total other income (expense), net	11,647	4,866	11,319	(16,824)	3,758	5,101	(4,848)	8,356	11,008	12,367	(12,707)
Income from continuing operations before income tax expense	(2,069)	27,156	28,086	50,315	(4,300)	24,075	21,936	51,178	103,488	92,889	79,840
Income tax expense (benefit)	(1,979)	7,060	6,607	13,453	(3,164)	6,069	5,322	13,613	25,141	21,840	18,267
Income from continuing operations	(90)	20,096	21,479	36,862	(1,136)	18,006	16,614	37,565	78,347	71,049	61,573
Loss from operations of discontinued operations, net of tax	(4)	(19)	(11)	(14)	(17)	(200)	(22)	(96)	(48)	(335)	(3)
Net income	$ (94)	$ 20,077	$ 21,468	$ 36,848	$ (1,153)	$ 17,806	$ 16,592	$ 37,469	$ 78,299	$ 70,714	$ 61,570
Basic:
Continuing operations (in dollars per share)	$ 0	$ 0.37	$ 0.40	$ 0.68	$ (0.02)	$ 0.33	$ 0.31	$ 0.69	$ 1.44	$ 1.31	$ 1.13
Discontinued operations (in dollars per share)	0	0	0	0	0	0	0	0	0	(0.01)	0
Net income (loss) (in dollars per share)	0	0.37	0.40	0.68	(0.02)	0.33	0.31	0.69	1.44	1.30	1.13
Diluted:
Continuing operations (in dollars per share)	0	0.36	0.39	0.66	(0.02)	0.32	0.30	0.67	1.42	1.27	1.09
Discontinued operations (in dollars per share)	0	0	0	0	0	0	0	0	(0.01)	(0.01)	0
Net income (loss) (in dollars per share)	$ 0	$ 0.36	$ 0.39	$ 0.66	$ (0.02)	$ 0.32	$ 0.30	$ 0.67	$ 1.41	$ 1.26	$ 1.09
Basic weighted average common shares outstanding (in shares)	54,039	54,403	54,142	54,571	54,547	54,268	54,090	54,287	54,288	54,299	54,561
Diluted weighted average common shares outstanding (in shares)	54,039	55,360	55,116	55,945	54,547	55,816	55,495	55,915	55,359	55,895	56,487