Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Revenue	$ 269,998	$ 266,090
Operating expenses	215,496	204,750
Gross margin	54,502	61,340
Corporate general and administrative expenses	11,680	10,028
Operating income	42,822	51,312
Other income (expense):
Interest expense	(1,401)	(1,780)
Gain on sale of operations, net	497	663
Other income (expense), net	9,260	(1,229)
Total other income (expense), net	8,356	(2,346)
Income from continuing operations before income tax expense	51,178	48,966
Income tax expense	13,613	13,156
Income from continuing operations	37,565	35,810
(Loss) income from discontinued operations, net of tax	(96)	41
Net income	$ 37,469	$ 35,851
Earnings per share - basic	$ 0.69	$ 0.66
Earnings per share - diluted	$ 0.67	$ 0.64
Basic weighted average shares outstanding	54,287	54,071
Diluted weighted average shares outstanding	55,915	55,924
Comprehensive income:
Net income	$ 37,469	$ 35,851
Other comprehensive income, net of tax	81	114
Comprehensive income	$ 37,550	$ 35,965