Consolidated Statements of Operations - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenues	[1]	$ 852,539	$ 1,163,314	$ 1,246,929
Operating expenses		613,828	835,570	918,673
Gross margin		238,711	327,744	328,256
Selling, general and administrative expenses		260,920	328,214	360,692
Restructuring and other related charges, net (see Note 16)		3,365	1,676	6,727
Gain on revaluation of contingent consideration		0	0	(202)
Goodwill impairment charge (see Note 7)		191,788	0	0
Operating loss		(217,362)	(2,146)	(38,961)
Interest expense, net		(29,818)	(29,713)	(30,875)
Loss on convertible debt embedded derivative (see Note 10)		0	0	(24,783)
Loss on debt extinguishment and modification		(2,224)	(279)	0
Other income (expense), net		(2,514)	(715)	410
Loss before income taxes		(251,918)	(32,853)	(94,209)
Benefit for income taxes (see Note 9)		14,715	436	31,063
Net loss		$ (237,203)	$ (32,417)	$ (63,146)
Loss per common share:
Net income (loss) (in USD per share)		$ (7.74)	$ (1.07)	$ (2.10)

[1] Revenues attributable to individual countries/geographic areas are based on the country of domicile of the legal entity that performs the work.