Segment Information (Segment Information) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 segments	Sep. 30, 2011
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)			3
Revenues from external sources	$ 2,779,600,000	$ 2,692,000,000	$ 8,451,300,000	$ 8,707,500,000
Intersegment revenues	0	0	0	0
Segment pretax income (loss)	29,376,000	92,940,000	23,226,000	98,263,000
Western Region Operations [Member]
Segment Reporting Information [Line Items]
Revenues from external sources	2,596,900,000	2,505,100,000	7,898,200,000	7,448,600,000
Intersegment revenues	2,700,000	3,000,000	8,300,000	8,900,000
Segment pretax income (loss)	20,200,000	71,800,000	12,600,000	207,100,000
Government Contracts [Member]
Segment Reporting Information [Line Items]
Revenues from external sources	169,800,000	175,900,000	527,400,000	1,222,000,000
Intersegment revenues	0	0	0	0
Segment pretax income (loss)	21,100,000	48,100,000	66,600,000	146,200,000
Divested Operations and Services [Member]
Segment Reporting Information [Line Items]
Revenues from external sources	12,900,000	11,000,000	25,700,000	36,900,000
Intersegment revenues	0	0	0	0
Segment pretax income (loss)	(4,700,000)	(22,400,000)	(34,400,000)	(58,900,000)
Corporate/Other/Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from external sources	0	0	0	0
Intersegment revenues	(2,700,000)	(3,000,000)	(8,300,000)	(8,900,000)
Segment pretax income (loss)	$ (7,200,000)	$ (4,600,000)	$ (21,600,000)	$ (196,100,000)