Business Segment Information - Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jul. 01, 2012	Jun. 30, 2013	Jul. 01, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 146,089	$ 155,297	$ 290,057	$ 306,956
Gross profit	25,269	25,508	52,068	49,325
Total SG&A	17,860	22,284	36,951	44,689
Total Operating income	7,409	3,224	15,117	4,636
Total Segment assets	376,929		376,929		373,409
Transportation [Member]
Segment Reporting Information [Line Items]
Revenues	80,000	83,800	155,100	164,400
Gross profit	13,700	14,500	29,100	27,900
Total SG&A	10,200	12,600	20,700	24,800
Total Operating income	3,500	1,900	8,400	3,100
Total Segment assets	178,800		178,800		172,900
Federal [Member]
Segment Reporting Information [Line Items]
Revenues	66,100	71,500	135,000	142,600
Gross profit	11,900	11,000	23,300	22,300
Total SG&A	7,700	9,700	16,300	19,900
Total Operating income	4,200	1,300	7,000	2,400
Total Segment assets	108,000		108,000		111,200
Corporate [Member]
Segment Reporting Information [Line Items]
Gross profit	(300)		(300)	(900)
Total Operating income	(300)		(300)	(900)
Total Segment assets	$ 90,100		$ 90,100		$ 89,300