Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenues	$ 1,792,430	$ 1,872,340	$ 3,506,167	$ 3,733,726
Cost of services (including depreciation)	1,592,213	1,644,835	3,102,637	3,268,315
Gross profit	200,217	227,505	403,530	465,411
Selling, general and administrative expenses	156,607	149,923	315,131	295,386
Amortization of intangible assets	8,141	8,731	15,636	17,024
Operating income	35,469	68,851	72,763	153,001
Interest expense	(3,583)	(1,675)	(7,172)	(3,075)
Interest income	641	319	1,157	772
Equity in losses of unconsolidated affiliates	(378)	(314)	(559)	(314)
Other income (expense), net	(725)	(134)	(463)	(346)
Income from continuing operations before income taxes	31,424	67,047	65,726	150,038
Provision for income taxes	14,695	31,584	28,138	62,185
Net income from continuing operations	16,729	35,463	37,588	87,853
Net income from discontinued operations		14,102		19,897
Net income	16,729	49,565	37,588	107,750
Less: Net income attributable to non-controlling interests	167	3,456	530	8,157
Net income attributable to common stock	16,562	46,109	37,058	99,593
Amounts attributable to common stock:
Net income from continuing operations	16,562	32,007	37,058	79,696
Net income from discontinued operations		14,102		19,897
Net income attributable to common stock	$ 16,562	$ 46,109	$ 37,058	$ 99,593
Earnings per share attributable to common stock - basic and diluted:
Continuing operations	$ 0.11	$ 0.15	$ 0.23	$ 0.37
Discontinued operations		0.07		0.09
Net income attributable to common stock	$ 0.11	$ 0.22	$ 0.23	$ 0.46
Shares used in computing earnings per share:
Weighted average basic shares outstanding	156,128	213,047	159,577	214,257
Weighted average diluted shares outstanding	156,130	213,059	159,579	214,269