Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Revenue	$ 750,422	$ 719,483	$ 677,171
Operating expenses	653,944	629,804	593,339
Gross margin	96,478	89,679	83,832
Corporate general and administrative expenses	32,594	34,183	34,398
Operating income	63,884	55,496	49,434
Other income (expense):
Interest expense	(8,902)	(13,124)	(15,374)
Gain on sale of operations, net	84	1,303	79
Other income, net	2,766	6,893	7,817
Total other expense, net	(6,052)	(4,928)	(7,478)
Income from continuing operations before income tax expense	57,832	50,568	41,956
Income tax expense	22,829	20,154	16,577
Income from continuing operations	35,003	30,414	25,379
(Loss) income from operations of discontinued operations, net of tax	(2,323)	(754)	2,148
Gain on disposal of discontinued operations, net of tax	1,427	99	58,336
Net income	$ 34,107	$ 29,759	$ 85,863
Basic:
Continuing operations	$ 0.70	$ 0.63	$ 0.52
Discontinued operations	(0.01)	(0.01)	1.25
Net income	0.69	0.62	1.77
Diluted:
Continuing operations	0.66	0.59	0.52
Discontinued operations	(0.01)	(0.01)	1.23
Net income	$ 0.65	$ 0.58	$ 1.75
Basic weighted average common shares outstanding	50,280	48,343	48,632
Diluted weighted average common shares outstanding	52,693	51,487	49,141
Comprehensive income:
Net income	$ 34,107	$ 29,759	$ 85,863
Other comprehensive income:
Net unrealized loss on available-for-sale securities, net of income tax benefit of $77, $74 and $97	(114)	(117)	(142)
Net unrealized gain on interest rate swaps, net of income tax expense of $135, $121 and $135	230	206	230
Foreign currency translation	(54)	(59)	(60)
Total other comprehensive income	62	30	28
Total comprehensive income	$ 34,169	$ 29,789	$ 85,891