Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Revenue	$ 235,498	$ 232,641	$ 505,496	$ 498,731
Operating expenses	198,148	205,102	413,644	409,852
Gross margin	37,350	27,539	91,852	88,879
Corporate general and administrative expenses	10,566	9,993	22,246	20,021
Operating income	26,784	17,546	69,606	68,858
Other (expense) income:
Interest expense	(1,587)	(1,817)	(2,988)	(3,597)
Gain on sale of operations, net	50		547	663
Other (expense) income, net	(3,311)	630	5,949	(599)
Total other (expense) income, net	(4,848)	(1,187)	3,508	(3,533)
Income from continuing operations before income tax expense	21,936	16,359	73,114	65,325
Income tax expense	5,322	3,238	18,935	16,394
Income from continuing operations	16,614	13,121	54,179	48,931
(Loss) gain from discontinued operations, net of tax	(22)	(15)	(118)	26
Net income	$ 16,592	$ 13,106	$ 54,061	$ 48,957
Basic:
Continuing operations	$ 0.31	$ 0.24	$ 1.00	$ 0.90
Net income	0.31	0.24	1.00	0.90
Diluted:
Continuing operations	0.30	0.23	0.97	0.87
Net income	$ 0.30	$ 0.23	$ 0.97	$ 0.87
Basic weighted average shares outstanding	54,090	54,594	54,188	54,334
Diluted weighted average shares outstanding	55,495	56,437	55,701	56,166
Comprehensive income:
Net income	$ 16,592	$ 13,106	$ 54,061	$ 48,957
Other comprehensive income, net of tax	(422)	174	(341)	288
Comprehensive income	$ 16,170	$ 13,280	$ 53,720	$ 49,245