Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Revenue	$ 300,730	$ 277,455
Operating expenses	223,971	199,827
Gross margin	76,759	77,628
Corporate general and administrative expenses	14,483	10,489
Operating income	62,276	67,139
Other income (expense):
Interest expense	(877)	(1,119)
Gain on sale of operations, net	0	95
Other income (expense), net	4,789	(15,800)
Total other income (expense), net	3,912	(16,824)
Income from continuing operations before income tax    expense	66,188	50,315
Income tax expense	15,972	13,453
Income from continuing operations	50,216	36,862
Loss from discontinued operations, net of tax	(7)	(14)
Net income	$ 50,209	$ 36,848
Basic:
Continuing operations (in dollars per share)	$ 0.94	$ 0.68
Discontinued operations (in dollars per share)	0	0
Net income (in dollars per share)	0.94	0.68
Diluted:
Continuing operations (in dollars per share)	0.92	0.66
Discontinued operations (in dollars per share)	0	0
Net income (in dollars per share)	$ 0.92	$ 0.66
Basic weighted average shares outstanding (in shares)	53,366	54,571
Diluted weighted average shares outstanding (in shares)	54,436	55,945
Comprehensive income:
Net income	$ 50,209	$ 36,848
Other comprehensive income (loss), net of tax	854	(1,252)
Comprehensive income	$ 51,063	$ 35,596