Segment Information (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 4,163,623	$ 3,421,392	$ 8,053,519	$ 6,460,327
Pretax income	132,102	98,802	199,811	160,762
Segment net income (loss)	58,368	120,867	88,356	149,654
Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Western Region Operations [Member]
Segment Reporting Information [Line Items]
Revenues	4,022,600	3,267,300	7,757,800	6,162,100
Pretax income	154,700	80,700	256,700	133,700
Segment net income (loss)	72,400	37,800	123,100	61,400
Western Region Operations [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	3,400	3,100	6,800	6,100
Government Contracts [Member]
Segment Reporting Information [Line Items]
Revenues	141,000	154,100	295,700	298,200
Pretax income	3,800	21,400	16,800	34,500
Segment net income (loss)	2,200	12,500	9,800	20,100
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	(26,400)	(3,300)	(73,700)	(7,400)
Segment net income (loss)	(16,200)	70,600	(44,500)	68,100
Corporate/Other/Eliminations [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	$ (3,400)	$ (3,100)	$ (6,800)	$ (6,100)