Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of unaudited quarterly results of operations
Revenue	$ 172,861	$ 183,800	$ 188,606	$ 220,827	$ 162,923	$ 177,349	$ 183,464	$ 210,069	$ 766,094	$ 733,805	$ 730,401
Operating expenses	166,353	167,146	166,695	180,005	159,802	154,345	160,345	169,727	680,195	644,269	644,335
Gross margin	6,508	16,654	21,915	40,822	3,121	23,004	23,069	40,342	85,899	89,536	86,066
Corporate general and administrative expenses	4,615	7,625	7,638	10,544	7,200	8,079	6,744	9,560	30,422	31,583	29,584
Operating income (loss)	1,893	9,029	14,277	30,278	(4,079)	14,925	16,325	30,782	55,477	57,953	56,482
Other income (expense):
Interest expense	(4,110)	(3,884)	(4,146)	(4,122)	(3,984)	(4,049)	(4,407)	(4,915)	(16,262)	(17,355)	(15,308)
Gain on sale of operations, net	106	21	50	2,589	88	87	2	2,743	2,766	2,920	466
Other income (expense), net	3,254	2,570	(840)	3,438	4,851	(4,510)	27	3,081	8,422	3,449	3,532
Total other income (expense), net	(750)	(1,293)	(4,936)	1,905	955	(8,472)	(4,378)	909	(5,074)	(10,986)	(11,310)
Income (loss) from continuing operations before income tax expense (benefit)	1,143	7,736	9,341	32,183	(3,124)	6,453	11,947	31,691	50,403	46,967	45,172
Income tax expense (benefit)	(58)	2,458	3,512	13,416	(1,913)	1,614	5,095	13,587	19,328	18,383	17,017
Income (loss) from continuing operations	1,201	5,278	5,829	18,767	(1,211)	4,839	6,852	18,104	31,075	28,584	28,155
(Loss) income from operations of discontinued operations, net of tax	(13)	(3)	1	(4)	25	(46)	(331)	(239)	(19)	(591)	(2,668)
Gain (loss) on disposal of discontinued operations, net of tax	18	32	18	22	20	(76)	30	40	90	14	(973)
Net Income (loss)	$ 1,206	$ 5,307	$ 5,848	$ 18,785	$ (1,166)	$ 4,717	$ 6,551	$ 17,905	$ 31,146	$ 28,007	$ 24,514
Basic:
Continuing operations	$ 0.02	$ 0.11	$ 0.12	$ 0.38	$ (0.02)	$ 0.10	$ 0.14	$ 0.37	$ 0.63	$ 0.58	$ 0.49
Discontinued operations							$ (0.01)	$ (0.01)		$ (0.01)	$ (0.07)
Net income	$ 0.02	$ 0.11	$ 0.12	$ 0.38	$ (0.02)	$ 0.10	$ 0.13	$ 0.36	$ 0.63	$ 0.57	$ 0.42
Diluted:
Continuing operations	$ 0.02	$ 0.11	$ 0.12	$ 0.38	$ (0.02)	$ 0.10	$ 0.14	$ 0.36	$ 0.63	$ 0.58	$ 0.48
Discontinued operations							$ (0.01)			$ (0.02)	$ (0.06)
Net income	$ 0.02	$ 0.11	$ 0.12	$ 0.38	$ (0.02)	$ 0.10	$ 0.13	$ 0.36	$ 0.63	$ 0.56	$ 0.42
Basic weighted average common shares outstanding	48,967	48,895	49,041	49,103	48,854	49,525	49,615	49,322	49,002	49,328	57,692
Diluted weighted average common shares outstanding	49,326	49,109	49,244	49,531	48,854	49,920	49,958	49,755	49,252	49,599	58,193