CONSOLIDATED STATEMENTS OF EQUITY - USD ($)	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)	Non-controlling interests not subject to put provisions
Temporary equity, beginning balance at Dec. 31, 2014		$ 829,965,000
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income		96,510,000
Distributions		(103,355,000)
Contributions		25,795,000
Acquisitions and divestitures		10,654,000
Partial purchases		(8,538,000)
Fair value remeasurement		13,035,000
Temporary equity, ending balance at Dec. 31, 2015		864,066,000
Beginning balance (in shares) at Dec. 31, 2014			215,641,000							0
Beginning balance at Dec. 31, 2014			$ 216,000			$ 1,108,211,000			$ 4,087,103,000	$ 0			$ (25,017,000)	$ 5,170,513,000		$ 189,798,000
Comprehensive income:
Net income									269,732,000					269,732,000		61,168,000
Other comprehensive income	$ (34,809,000)												(34,809,000)	(34,809,000)
Stock purchase shares issued (in shares)										414,000
Stock purchase shares issued						(6,079,000)				$ 30,608,000				24,529,000
Stock-settled share based payment awards, shares issued (in shares)				348,000	1,131,000
Stock-settled share based payment awards					$ 1,000			$ (1,000)
Stock-settled stock-based compensation expense						56,899,000								56,899,000
Excess tax benefits from stock awards exercised						28,157,000								28,157,000
Distributions																(71,280,000)
Contributions																28,849,000
Acquisitions and divestitures, noncontrolling interest																6,875,000
Partial purchases						(55,826,000)								(55,826,000)		(2,018,000)
Fair value remeasurements						(13,035,000)								(13,035,000)
Purchase of treasury stock (in shares)										(7,780,000)
Purchase of treasury stock	(575,380,000)									$ (575,380,000)
Ending balance at Dec. 31, 2015			$ 217,000			1,118,326,000			4,356,835,000	$ (544,772,000)			(59,826,000)	4,870,780,000		213,392,000
Ending balance (in shares) at Dec. 31, 2015			217,120,000							(7,366,000)
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income		99,834,000
Distributions		(111,092,000)
Contributions		33,517,000
Acquisitions and divestitures		28,874,000
Partial purchases		(6,660,000)
Fair value remeasurement		65,855,000
Reclassifications of Temporary to Permanent Equity		(1,136,000)														1,136,000
Temporary equity, ending balance at Dec. 31, 2016		973,258,000
Comprehensive income:
Net income									879,874,000					879,874,000		53,374,000
Other comprehensive income	$ (29,627,000)												(29,817,000)	(29,817,000)		190,000
Stock purchase shares issued (in shares)			438,000
Stock purchase shares issued			$ 1,000			23,902,000								23,903,000
Stock-settled share based payment awards, shares issued (in shares)				4,000	218,000						276,000	513,000
Stock-settled share based payment awards							$ (19,815,000)	$ (36,685,000)			$ 19,815,000	$ 36,685,000
Stock-settled stock-based compensation expense						37,970,000								37,970,000
Excess tax benefits from stock awards exercised						13,251,000								13,251,000
Distributions																(81,309,000)
Contributions																14,073,000
Acquisitions and divestitures						3,423,000								3,423,000
Acquisitions and divestitures, noncontrolling interest																2,585,000
Partial purchases						(13,105,000)								(13,105,000)		(1,747,000)
Fair value remeasurements						(65,855,000)								(65,855,000)
Reclassifications and expirations of puts		1,136,000														(1,136,000)
Purchase of treasury stock (in shares)	(16,649,090)									(16,649,000)
Purchase of treasury stock	$ (1,072,377,000)									$ (1,072,377,000)				(1,072,377,000)
Retirement of treasury stock (in shares)			(23,226,000)							23,226,000
Retirement of treasury stock			$ (23,000)			(34,230,000)			(1,526,396,000)	$ 1,560,649,000
Ending balance at Dec. 31, 2016	$ 4,849,741,000		$ 195,000			1,027,182,000			3,710,313,000	$ 0			(89,643,000)	4,648,047,000		201,694,000
Ending balance (in shares) at Dec. 31, 2016	194,554,491		194,554,000							0
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income		103,641,000
Distributions		(128,853,000)
Contributions		52,911,000
Acquisitions and divestitures		43,799,000
Partial purchases		(397,000)
Fair value remeasurement		(32,999,000)
Temporary equity, ending balance at Dec. 31, 2017		$ 1,011,360,000
Comprehensive income:
Net income									663,618,000					663,618,000		63,296,000
Other comprehensive income	$ 102,876,000												102,878,000	102,878,000		(2,000)
Stock purchase shares issued (in shares)			360,000
Stock purchase shares issued						22,131,000								22,131,000
Stock-settled share based payment awards, shares issued (in shares)				117,000	398,000
Stock-settled share based payment awards							$ (101,000)								$ (101,000)
Stock-settled stock-based compensation expense						34,981,000								34,981,000
Distributions																(82,614,000)
Contributions																21,641,000
Acquisitions and divestitures						823,000								823,000
Acquisitions and divestitures, noncontrolling interest																5,770,000
Partial purchases						(2,752,000)								(2,752,000)		(2,208,000)
Fair value remeasurements						32,999,000								32,999,000
Purchase of treasury stock (in shares)	(12,966,672)									(12,967,000)
Purchase of treasury stock	$ (810,949,000)									$ (810,949,000)				(810,949,000)
Retirement of treasury stock (in shares)			(12,967,000)							12,967,000
Retirement of treasury stock			$ (13,000)			(70,718,000)			(740,218,000)	$ 810,949,000
Ending balance at Dec. 31, 2017	$ 4,886,066,000		$ 182,000			$ 1,042,899,000			$ 3,633,713,000	$ 0			$ 13,235,000	$ 4,690,029,000		$ 196,037,000
Ending balance (in shares) at Dec. 31, 2017	182,462,278		182,462,000							0