Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Shares $1 Par Value	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Subtotal	Non-controlling Interests
Beginning balance at Dec. 31, 2014	$ 10,370,022	$ 367,499	$ 5,059,508	$ 447,082	$ 4,428,069	$ 10,302,158	$ 67,864
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	274,591				279,587	279,587	(4,996)
Other comprehensive income (loss), net of taxes	(8,289)			(8,289)		(8,289)
Contributions from noncontrolling interests	16,189					0	16,189
Distributions to noncontrolling interests	(7,277)					0	(7,277)
Deconsolidation of asset management entities	(8,193)					0	(8,193)
Change in interest in consolidated subsidiary	0		(1,092)			(1,092)	1,092
Share-based compensation expense	74,087		74,087			74,087
Change in fair value of redeemable noncontrolling interests	(26,325)		(26,325)			(26,325)
Purchase of common shares for treasury	(125,754)	(5,953)	(119,801)			(125,754)
Dividends ($.25, $.25 and $.325 per common share for year ended 2015, 2016, 2017)	(94,674)				(94,674)	(94,674)
Other	1,513	1,071	442			1,513
Ending balance at Dec. 31, 2015	10,465,890	362,617	4,986,819	438,793	4,612,982	10,401,211	64,679
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	124,512				125,938	125,938	(1,426)
Other comprehensive income (loss), net of taxes	(128,096)			(128,096)		(128,096)
Contributions from noncontrolling interests	154,522					0	154,522
Distributions to noncontrolling interests	(18,544)					0	(18,544)
Deconsolidation of asset management entities	(9,709)					0	(9,709)
Change in interest in consolidated subsidiary	0		(261)			(261)	261
Reclassification to redeemable noncontrolling interest	(14,234)					0	(14,234)
Share-based compensation expense	33,597		33,597			33,597
Change in fair value of redeemable noncontrolling interests	(115,963)		(115,963)			(115,963)
Purchase of common shares for treasury	(95,020)	(5,434)	(89,586)			(95,020)
Dividends ($.25, $.25 and $.325 per common share for year ended 2015, 2016, 2017)	(93,529)				(93,529)	(93,529)
Other	223	2,242	(2,019)			223
Ending balance at Dec. 31, 2016	10,303,649	359,425	4,812,587	310,697	4,645,391	10,128,100	175,549
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	163,896				167,351	167,351	(3,455)
Other comprehensive income (loss), net of taxes	71,227			71,227		71,227
Contributions from noncontrolling interests	40,072					0	40,072
Distributions to noncontrolling interests	(12,031)					0	(12,031)
Deconsolidation of real estate entity	(167,163)					0	(167,163)
Share-based compensation expense	48,384		48,384			48,384
Change in fair value of redeemable noncontrolling interests	(94,937)		(94,937)			(94,937)
Purchase of common shares for treasury	(100,477)	(4,024)	(96,453)			(100,477)
Dividends ($.25, $.25 and $.325 per common share for year ended 2015, 2016, 2017)	(120,974)				(120,974)	(120,974)
Other	7,333	826	6,457			7,283	50
Ending balance at Dec. 31, 2017	10,138,979	$ 356,227	$ 4,676,038	372,724	4,700,968	$ 10,105,957	$ 33,022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of tax effects from accumulated other comprehensive income	$ 0			$ (9,200)	$ 9,200