Business Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Business segments
Revenue	$ 145,237	$ 131,139	$ 452,193	$ 382,233
Total gross profit	22,774	27,117	72,099	75,642
Total SG&A	(21,385)	(17,749)	(66,073)	(56,982)
Total operating income	1,389	9,368	6,026	18,660
Total Segment assets	382,365		382,365		379,874
Transportation [Member]
Business segments
Revenue	78,300	76,200	242,700	219,400
Total gross profit	13,500	14,000	41,400	38,400
Total SG&A	(11,900)	(11,100)	(36,700)	(35,100)
Total operating income	1,600	2,900	4,700	3,300
Total Segment assets	187,300		187,300		182,100
Federal [Member]
Business segments
Revenue	66,900	54,900	209,500	162,800
Total gross profit	9,800	13,500	32,100	38,000
Total SG&A	(9,500)	(6,600)	(29,400)	(21,900)
Total operating income	300	6,900	2,700	16,100
Total Segment assets	116,200		116,200		133,600
Corporate [Member]
Business segments
Total gross profit	(500)	(400)	(1,400)	(700)
Total operating income	(500)	(400)	(1,400)	(700)
Total Segment assets	$ 78,900		$ 78,900		$ 64,200