CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]	Redeemable Noncontrolling Interests [Member]
Balances at Dec. 31, 2016		$ 2,034	$ 2,381,011	$ (1,073,457)	$ (6,865)	$ (176,707)	$ 223,500
Balances (in shares) at Dec. 31, 2016		203,396,066
Equity [Roll Forward]
Non-cash and stock-based compensation	$ 42,755		42,755	0
Common stock issued under stock plans, net of shares withheld for employee taxes	(5,452)	$ 4	(5,456)
Common stock issued under stock plans, net of shares withheld for employee taxes (in shares)		342,974
Exercise of stock options	51,069	$ 31	51,038
Exercise of stock options (in shares)		3,137,997
Acquisitions	9,159						9,159
Purchases of noncontrolling interests	(6,452)		(3,616)				(2,836)
Redeemable noncontrolling interests adjustments	(91,631)		(91,631)
Contributions received	10,671						10,671
Cash distributions	(24,715)						(24,715)
Other	117		(95)				212
Other comprehensive income (loss), net of tax:
Net income (loss)	14,942			(6,015)			20,957
Foreign currency translation adjustments	67,704					67,704
Other	461					461
Balances at Dec. 31, 2017	1,418,144	$ 2,069	2,374,006	(1,079,472)	(6,865)	(108,542)	236,948
Balances (in shares) at Dec. 31, 2017		206,877,037
Balances at Dec. 31, 2016								$ 347,068
Redeemable Noncontrolling Interests [Roll Forward]
Acquisitions								6,640
Purchase of noncontrolling interests								(165,227)
Redeemable noncontrolling interests fair value adjustments								91,631
Contributions received								1,875
Cash distributions								(28,994)
Other								(1,099)
Comprehensive income (loss):
Net income (loss)								(7,167)
Balances at Dec. 31, 2017								244,727
Equity [Roll Forward]
Non-cash and stock-based compensation	45,715		45,715
Common stock issued under stock plans, net of shares withheld for employee taxes	(12,456)	$ 4	(12,460)
Common stock issued under stock plans, net of shares withheld for employee taxes (in shares)		434,707
Exercise of stock options	(24,327)	$ 18	(24,345)
Exercise of stock options (in shares)		1,823,809
Conversion of convertible debt (in shares)		28
Fair value of convertible debt conversion feature, net of issuance costs	62,639		62,639
Repurchase of convertible debt conversion feature	(92,641)		(92,641)
Acquisitions	33,564						33,564
Divestitures	(6,684)						(6,684)
Purchases of noncontrolling interests	(13,087)		(8,210)				(4,877)
Sales of noncontrolling interests	452		1,410				(958)
Redeemable noncontrolling interests adjustments	(77,799)		(77,799)
Contributions received	7,501						7,501
Cash distributions	(43,346)						(43,346)
Other	(2,075)		(106)				(1,969)
Other comprehensive income (loss), net of tax:
Net income (loss)	83,832			60,249			23,583
Foreign currency translation adjustments	(36,689)					(36,689)
Other	0					0
Balances at Dec. 31, 2018	$ 1,342,743	$ 2,091	2,268,209	(1,019,223)	(6,865)	(145,231)	243,762
Balances (in shares) at Dec. 31, 2018	209,135,581	209,135,581
Redeemable Noncontrolling Interests [Roll Forward]
Acquisitions								25,542
Purchase of noncontrolling interests								(10,356)
Sales of Noncontrolling Interest								0
Redeemable noncontrolling interests fair value adjustments								77,799
Contributions received								1,806
Cash distributions								(15,840)
Other								(831)
Comprehensive income (loss):
Net income (loss)								6,508
Balances at Dec. 31, 2018	$ 329,355							329,355
Equity [Roll Forward]
Non-cash and stock-based compensation	48,887		48,887
Common stock issued under stock plans, net of shares withheld for employee taxes	(15,352)	$ 5	(15,357)
Common stock issued under stock plans, net of shares withheld for employee taxes (in shares)		392,147
Exercise of stock options	14,104	$ 9	14,095
Exercise of stock options (in shares)		910,006
Conversion of convertible debt	28,586	$ 8	28,578
Conversion of convertible debt (in shares)		824,328
Acquisitions	137,981						137,981
Purchases of noncontrolling interests	(48,745)		(23,878)				(24,867)
Redeemable noncontrolling interests adjustments	(74,771)		(74,771)
Contributions received	14,285						14,285
Cash distributions	(84,115)						(84,115)
Other	(2,323)		(144)				(2,179)
Other comprehensive income (loss), net of tax:
Net income (loss)	103,156			69,889			33,267
Foreign currency translation adjustments	(482)					(482)
Other	0
Balances at Dec. 31, 2019	$ 1,463,954	$ 2,113	$ 2,245,619	$ (949,334)	$ (6,865)	$ (145,713)	$ 318,134
Balances (in shares) at Dec. 31, 2019	211,262,062	211,262,062
Redeemable Noncontrolling Interests [Roll Forward]
Acquisitions								52,373
Purchase of noncontrolling interests								(1,459)
Redeemable noncontrolling interests fair value adjustments								74,771
Contributions received								0
Cash distributions								(23,362)
Other								2,764
Comprehensive income (loss):
Net income (loss)								15,056
Balances at Dec. 31, 2019	$ 449,498							$ 449,498