CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock Issued [Member]	Treasury Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Loss [Member]	Non-controlling interest [Member]
Beginning Balance, Shares at Dec. 31, 2017		269,335	(88,504)
Beginning Balance at Dec. 31, 2017	$ 1,160,072	$ 2,693	$ (322,735)	$ 1,781,059	$ (338,150)	$ (1,985)	$ 39,190
Stock-based compensation				9,935
Common stock issued under stock compensation plans, net of shares withheld for employee taxes, Shares		1,266
Common stock issued under stock compensation plans, net of shares withheld for employee taxes		$ 13		(8,296)
Issuance of treasury stock, Shares			0
Accretion of redemption preference on redeemable convertible non-controlling interest - discontinued operations				(12,149)
Subsidiary issuance of common stock				(430)
Purchase of treasury stock, Shares			(4,144)
Purchase of treasury stock			$ (57,600)
Warrants issued				682
Net loss less net income attributable to non-controlling interests					(27,725)
ASC 606 implementation adjustments					46,604
Foreign currency translation adjustments, net	123					123
Unrecognized gain on derivatives qualifying as cash flow hedges, net of tax						(319)
Acquisition of non-controlling interest				0			0
Net loss attributable to non-controlling interests	(790)						(790)
Ending Balance, Shares at Mar. 31, 2018		270,601	(92,648)
Ending Balance at Mar. 31, 2018	1,110,120	$ 2,706	$ (380,335)	1,770,801	(319,271)	(2,181)	38,400
Beginning Balance, Shares at Dec. 31, 2017		269,335	(88,504)
Beginning Balance at Dec. 31, 2017	$ 1,160,072	$ 2,693	$ (322,735)	1,781,059	(338,150)	(1,985)	39,190
Common stock issued under stock compensation plans, net of shares withheld for employee taxes, Shares	1,600
Ending Balance, Shares at Dec. 31, 2018	270,955	270,955	(99,731)
Ending Balance at Dec. 31, 2018	$ 1,580,427	$ 2,709	$ (460,543)	1,881,494	132,842	(5,389)	29,314
Stock-based compensation				11,394
Common stock issued under stock compensation plans, net of shares withheld for employee taxes, Shares	1,100	1,058
Common stock issued under stock compensation plans, net of shares withheld for employee taxes		$ 10		(5,338)
Issuance of treasury stock, Shares			0
Accretion of redemption preference on redeemable convertible non-controlling interest - discontinued operations				0
Subsidiary issuance of common stock				0
Purchase of treasury stock, Shares			(6,148)
Purchase of treasury stock			$ (65,070)
Warrants issued				682
Net loss less net income attributable to non-controlling interests					(7,553)
ASC 606 implementation adjustments					0
Foreign currency translation adjustments, net	$ 695					695
Unrecognized gain on derivatives qualifying as cash flow hedges, net of tax						97
Acquisition of non-controlling interest				(29,913)			(28,890)
Net loss attributable to non-controlling interests	$ (424)						(424)
Ending Balance, Shares at Mar. 31, 2019	272,013	272,013	(105,879)
Ending Balance at Mar. 31, 2019	$ 1,456,117	$ 2,719	$ (525,613)	$ 1,858,319	$ 125,289	$ (4,597)	$ 0