Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Revenues	$ 1,872,340	$ 1,838,209	$ 3,733,726	$ 3,573,657
Cost of services (including depreciation)	1,644,835	1,574,000	3,268,315	3,053,394
Gross profit	227,505	264,209	465,411	520,263
Selling, general and administrative expenses	149,923	135,210	295,386	304,099
Amortization of intangible assets	8,731	8,202	17,024	16,035
Operating income	68,851	120,797	153,001	200,129
Interest expense	(1,675)	(1,128)	(3,075)	(2,110)
Interest income	319	599	772	2,141
Equity in earnings (losses) of unconsolidated affiliates	(314)	(332)	(314)	(332)
Other income (expense), net	(134)	(901)	(346)	(257)
Income from continuing operations before income taxes	67,047	119,035	150,038	199,571
Provision for income taxes	31,584	41,220	62,185	70,074
Net income from continuing operations	35,463	77,815	87,853	129,497
Net income from discontinued operations	14,102	7,629	19,897	14,595
Net income	49,565	85,444	107,750	144,092
Less: Net income attributable to non-controlling interests	3,456	4,362	8,157	8,602
Net income attributable to common stock	46,109	81,082	99,593	135,490
Amounts attributable to common stock:
Net income from continuing operations	32,007	73,453	79,696	120,895
Net income from discontinued operations	14,102	7,629	19,897	14,595
Net income attributable to common stock	$ 46,109	$ 81,082	$ 99,593	$ 135,490
Earnings per share attributable to common stock-basic and diluted:
Continuing operations	$ 0.15	$ 0.33	$ 0.37	$ 0.55
Discontinued operations	0.07	0.04	0.09	0.07
Net income attributable to common stock	$ 0.22	$ 0.37	$ 0.46	$ 0.62
Shares used in computing earnings per share:
Weighted average basic shares outstanding	213,047	219,612	214,257	219,345
Weighted average diluted shares outstanding	213,059	219,642	214,269	219,375