Segment Information (Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 3,421,392	$ 2,738,431	$ 6,460,327	$ 5,535,468
Pretax income	98,802	52,028	160,762	133,331
Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Western Region Operations [Member]
Segment Reporting Information [Line Items]
Revenues	3,267,300	2,598,500	6,162,100	5,261,000
Pretax income	80,700	46,800	133,700	119,100
Western Region Operations [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	3,100	2,800	6,100	5,700
Government Contracts [Member]
Segment Reporting Information [Line Items]
Revenues	154,100	139,900	298,200	274,500
Pretax income	21,400	18,100	34,500	27,100
Government Contracts [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Corporate/Other/Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Pretax income	(3,300)	(12,900)	(7,400)	(12,900)
Corporate/Other/Eliminations [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	$ (3,100)	$ (2,800)	$ (6,100)	$ (5,700)