Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Revenue	$ 232,641	$ 211,016	$ 498,731	$ 452,475
Operating expenses	205,102	188,120	409,852	380,886
Gross margin	27,539	22,896	88,879	71,589
Corporate general and administrative expenses	9,993	9,232	20,021	18,000
Operating income (loss)	17,546	13,664	68,858	53,589
Other (expense) income:
Interest expense	(1,817)	(1,692)	(3,597)	(3,209)
Gain on sale of operations, net		23	663	45
Other income (expense), net	630	3,764	(599)	6,501
Total other (expense) income, net	(1,187)	2,095	(3,533)	3,337
Income from continuing operations before income tax expense	16,359	15,759	65,325	56,926
Income tax expense	3,238	4,343	16,394	20,484
Income from continuing operations	13,121	11,416	48,931	36,442
(Loss) gain from discontinued operations, net of tax	(15)	(418)	26	(570)
Net income	$ 13,106	$ 10,998	$ 48,957	$ 35,872
Basic:
Continuing operations	$ 0.24	$ 0.21	$ 0.90	$ 0.68
Discontinued operations		(0.01)		(0.01)
Net income	0.24	0.20	0.90	0.67
Diluted:
Continuing operations	0.23	0.20	0.87	0.66
Discontinued operations		(0.01)		(0.01)
Net income	$ 0.23	$ 0.19	$ 0.87	$ 0.65
Basic weighted average shares outstanding	54,594	53,968	54,334	53,632
Diluted weighted average shares outstanding	56,437	55,831	56,166	55,530
Comprehensive income:
Net income	$ 13,106	$ 10,998	$ 48,957	$ 35,872
Other comprehensive income, net of tax	174	37	288	217
Comprehensive income	$ 13,280	$ 11,035	$ 49,245	$ 36,089