CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Non-controlling interests subject to put provisions	Common stock	Common stock Restricted Stock Units (RSUs)	Common stock Stock appreciation rights	Additional paid-in capital	Additional paid-in capital Restricted Stock Units (RSUs)	Additional paid-in capital Stock appreciation rights	Retained earnings	Treasury stock	Treasury stock Restricted Stock Units (RSUs)	Treasury stock Stock appreciation rights	Accumulated other comprehensive income (loss)	Total	Total Restricted Stock Units (RSUs)	Total Stock appreciation rights	Non-controlling interests not subject to put provisions
Temporary equity, beginning balance at Dec. 31, 2015		$ 864,066
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income		99,834
Distributions		(111,092)
Contributions		33,517
Acquisitions and divestitures		28,874
Partial purchases		(6,660)
Fair value remeasurements		65,855
Reclassifications of Temporary to Permanent Equity		(1,136)															$ 1,136
Temporary equity, ending balance at Dec. 31, 2016		973,258
Beginning balance (in shares) at Dec. 31, 2015			(217,120,000)							(7,366,000)
Beginning balance at Dec. 31, 2015			$ 217			$ 1,118,326			$ 4,356,835	$ (544,772)			$ (59,826)	$ 4,870,780			213,392
Comprehensive income:
Net income	$ 879,874								879,874					879,874			53,374
Comprehensive income	(29,627)												(29,817)	(29,817)			190
Stock purchase shares issued (in shares)			438,000
Stock purchase shares issued			$ 1			23,902								23,903
Stock-settled share based payment awards, shares issued (in shares)				4,000	218,000						276,000	513,000
Stock-settled share based payment awards				$ 0	$ 0		$ 19,815	$ 36,685			$ 19,815	$ 36,685			$ 0	$ 0
Stock-settled stock-based compensation expense						37,970								37,970
Excess tax benefits from stock awards exercised						13,251								13,251
Distributions																	(81,309)
Contributions																	14,073
Acquisitions and divestitures						3,423								3,423
Acquisitions and divestitures, noncontrolling interest																	2,585
Partial purchases						(13,105)								(13,105)			(1,747)
Fair value remeasurements						(65,855)								(65,855)
Reclassifications and expirations of puts		1,136															(1,136)
Purchase of treasury stock (in shares)										(16,649,000)
Purchase of treasury stock										$ (1,072,377)				(1,072,377)
Retirement of treasury stock (in shares)			(23,226,000)							(23,226,000)
Retirement of treasury stock			$ (23)			(34,230)			(1,526,396)	$ 1,560,649
Ending balance at Dec. 31, 2016			$ 195			1,027,182			3,710,313	$ 0			(89,643)	4,648,047			201,694
Ending balance (in shares) at Dec. 31, 2016			(194,554,000)							0
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income		103,641
Distributions		(128,853)
Contributions		52,911
Acquisitions and divestitures		43,799
Partial purchases		(397)
Fair value remeasurements		(32,999)
Temporary equity, ending balance at Dec. 31, 2017		1,011,360
Comprehensive income:
Net income	663,618								663,618					663,618			63,296
Comprehensive income	$ 102,876												102,878	102,878			(2)
Stock purchase shares issued (in shares)			360,000
Stock purchase shares issued						22,131								22,131
Stock-settled share based payment awards, shares issued (in shares)				117,000	398,000
Stock-settled share based payment awards							101	0							101	0
Stock-settled stock-based compensation expense						34,981								34,981
Distributions																	(82,614)
Contributions																	21,641
Acquisitions and divestitures						(823)								(823)
Acquisitions and divestitures, noncontrolling interest																	(5,770)
Partial purchases						(2,752)								(2,752)			(2,208)
Fair value remeasurements						32,999								32,999
Purchase of treasury stock (in shares)	(12,966,672)									(12,967,000)
Purchase of treasury stock	$ (810,949)									$ (810,949)				(810,949)
Retirement of treasury stock (in shares)			(12,967,000)							(12,967,000)
Retirement of treasury stock			$ (13)			(70,718)			(740,218)	$ 810,949
Ending balance at Dec. 31, 2017	$ 4,886,066		$ 182			1,042,899			3,633,713	$ 0			13,235	4,690,029			196,037
Ending balance (in shares) at Dec. 31, 2017	(182,462,278)		(182,462,000)							0
Comprehensive income:
Cumulative Effect of New Accounting Principle in Period of Adoption									8,368				(8,368)	0
Net income		105,531
Distributions		(119,173)
Contributions		32,918
Acquisitions and divestitures		79,078
Partial purchases		(8,546)
Fair value remeasurements		23,473
Temporary equity, ending balance at Dec. 31, 2018		$ 1,124,641
Comprehensive income:
Net income	$ 159,394								159,394					159,394			68,115
Comprehensive income	$ (39,791)												(39,791)	(39,791)
Stock purchase shares issued (in shares)			398,000
Stock purchase shares issued						17,398								17,398
Stock-settled share based payment awards, shares issued (in shares)				158,000	213,000
Stock-settled share based payment awards					$ 1		$ 448	$ 4,887							$ 448	$ 4,886
Stock-settled stock-based compensation expense						73,081								73,081
Distributions																	(77,268)
Contributions																	19,393
Acquisitions and divestitures						3,546								3,546
Acquisitions and divestitures, noncontrolling interest																	318
Partial purchases						(17,897)								(17,897)			(1,639)
Fair value remeasurements						(23,473)								(23,473)
Purchase of treasury stock (in shares)	(16,844,067)									(16,844,000)
Purchase of treasury stock	$ (1,153,511)									$ (1,153,511)				(1,153,511)
Retirement of treasury stock (in shares)			(16,844,000)							(16,844,000)
Retirement of treasury stock			$ (17)			(95,213)			(1,058,281)	$ 1,153,511				0
Ending balance at Dec. 31, 2018	$ 3,908,398		$ 166			$ 995,006			$ 2,743,194	$ 0			$ (34,924)	$ 3,703,442			$ 204,956
Ending balance (in shares) at Dec. 31, 2018	(166,387,307)		(166,387,000)							0