Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Revenue	$ 719,483	$ 677,171	$ 612,689
Operating expenses	629,804	593,339	540,305
Gross margin	89,679	83,832	72,384
Corporate general and administrative expenses	34,183	34,398	30,209
Operating income	55,496	49,434	42,175
Other income (expense):
Interest expense	(13,124)	(15,374)	(14,999)
Gain on sale of operations, net	1,303	79	2,766
Other income, net	6,893	7,817	8,215
Total other expense, net	(4,928)	(7,478)	(4,018)
Income from continuing operations before income tax expense	50,568	41,956	38,157
Income tax expense	20,154	16,577	14,364
Income from continuing operations	30,414	25,379	23,793
(Loss) income from operations of discontinued operations, net of tax	(754)	2,148	7,263
Gain on disposal of discontinued operations, net of tax	99	58,336	90
Net income	29,759	85,863	31,146
Basic:
Continuing operations	$ 0.63	$ 0.52	$ 0.49
Discontinued operations	$ (0.01)	$ 1.25	$ 0.14
Net income	$ 0.62	$ 1.77	$ 0.63
Diluted:
Continuing operations	$ 0.59	$ 0.52	$ 0.48
Discontinued operations	$ (0.01)	$ 1.23	$ 0.15
Net income	$ 0.58	$ 1.75	$ 0.63
Basic weighted average common shares outstanding	48,343	48,632	49,002
Diluted weighted average common shares outstanding	51,487	49,141	49,252
Comprehensive income:
Net income	29,759	85,863	31,146
Other comprehensive income:
Net unrealized (loss) gain on available-for-sale securities, net of income tax (benefit) expense of $(74); $(97) and $120	(117)	(142)	181
Net unrealized gain (loss) on interest rate swaps, net of income tax expense (benefit) of $121; $135 and $(54)	206	230	(93)
Foreign currency translation	(59)	(60)	(62)
Total other comprehensive income	30	28	26
Total comprehensive income	$ 29,789	$ 85,891	$ 31,172