Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Revenue	$ 238,389	$ 239,790	$ 752,787	$ 745,286
Operating expenses	204,760	209,146	613,603	622,790
Gross margin	33,629	30,644	139,184	122,496
Corporate general and administrative expenses	11,339	11,670	32,988	33,916
Operating income	22,290	18,974	106,196	88,580
Other income (expense):
Interest expense	(974)	(1,521)	(4,167)	(4,509)
(Loss) gain on sale of operations, net	(74)	(145)	78	402
Other income, net	5,914	6,767	3,450	12,716
Total other income (expense), net	4,866	5,101	(639)	8,609
Income from continuing operations before income tax expense	27,156	24,075	105,557	97,189
Income tax expense	7,060	6,069	27,120	25,004
Income from continuing operations	20,096	18,006	78,437	72,185
Loss from discontinued operations, net of tax	(19)	(200)	(44)	(318)
Net income	$ 20,077	$ 17,806	$ 78,393	$ 71,867
Earnings (loss) per share Basic:
Continuing operations	$ 0.37	$ 0.33	$ 1.44	$ 1.33
Discontinued operations				(0.01)
Net income	0.37	0.33	1.44	1.32
Earnings (loss) per share Diluted:
Continuing operations	0.36	0.32	1.41	1.29
Discontinued operations				(0.01)
Net income	$ 0.36	$ 0.32	$ 1.41	$ 1.28
Basic weighted average shares outstanding	54,403	54,268	54,372	54,215
Diluted weighted average shares outstanding	55,360	55,816	55,473	55,778
Comprehensive income:
Net income	$ 20,077	$ 17,806	$ 78,393	$ 71,867
Other comprehensive loss, net of tax	(186)	(129)	(1,815)	(470)
Comprehensive income	$ 19,891	$ 17,677	$ 76,578	$ 71,397