Segment Information (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 4,153,667	$ 3,789,870	$ 12,207,186	$ 10,250,197
Pretax income	153,348	22,723	353,159	183,485
Segment net income (loss)	60,253	(8,939)	148,609	140,715
Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Western Region Operations [Member]
Segment Reporting Information [Line Items]
Revenues	3,993,000	3,643,700	11,750,800	9,805,800
Pretax income	172,600	105,900	429,300	239,600
Segment net income (loss)	73,700	44,800	196,800	106,200
Western Region Operations [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	3,400	3,100	10,200	9,200
Government Contracts [Member]
Segment Reporting Information [Line Items]
Revenues	160,700	146,200	456,400	444,400
Pretax income	2,500	22,600	19,300	57,100
Segment net income (loss)	1,400	13,700	11,200	33,800
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	(21,700)	(105,800)	(95,400)	(113,200)
Segment net income (loss)	(14,800)	(67,400)	(59,400)	700
Corporate/Other/Eliminations [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Revenues	$ (3,400)	$ (3,100)	$ (10,200)	$ (9,200)