Discontinued Operations and Assets Held for Sale - Summarized operating results of the Discontinued Operations (Details) - Discontinued Operations, Held-for-sale or Disposed of by Sale - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$ 869,670	$ 992,113	$ 942,329
Depreciation and amortization	26,515	60,409	65,073
Share-based compensation expense	1,053	2,944	2,957
Other direct costs	693,729	780,490	758,617
Loss on impairment of assets	0	33,476	23,465
Operating income	148,373	114,794	92,217
Other non-operating expense	(21,911)	(17,373)	(28,210)
Pretax income of discontinued operations	126,462	97,421	64,007
Income tax expense	(47,382)	(24,495)	(30,561)
Income from discontinued operations, net of tax	79,080	72,926	33,446
Operating cash flows of discontinued operations	171,209	121,259	106,752
Investing cash flows of discontinued operations	(71,397)	(74,435)	(46,790)
Financing cash flows of discontinued operations	$ (16,774)	$ (78,014)	$ (35,127)