Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance - beginning of period	$ 3,561,428	$ 3,890,735	$ 2,202,731
Amounts reclassified from accumulated other comprehensive income (loss) to:
Interest expense	183,409	194,326	178,122
Equity in earnings of equity method investments in the Managed Programs and real estate	64,719	51,020	44,116
Net current period other comprehensive income (loss)	(83,282)	(101,379)	(96,863)
Balance - end of period	3,425,140	3,561,428	3,890,735
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance - beginning of period	(172,291)	(75,559)	15,336
Reconciliation Of Accumulated Comprehensive Income [Abstract]
Other comprehensive income (loss) before reclassifications	(75,978)	(96,041)	(100,037)
Amounts reclassified from accumulated other comprehensive income (loss) to:
Amount reclassified from accumulated other comprehensive income (loss)	(7,304)	(5,338)	3,174
Net current period other comprehensive income (loss)	(83,282)	(101,379)	(96,863)
Net current period other comprehensive loss attributable to noncontrolling interests and redeemable noncontrolling interest	1,088	4,647	5,968
Balance - end of period	(254,485)	(172,291)	(75,559)
Accumulated Other Comprehensive Income (Loss) | Amounts reclassified from accumulated other comprehensive income (loss) to:
Amounts reclassified from accumulated other comprehensive income (loss) to:
Interest expense	2,106	2,291	2,691
Other income and (expenses)	(9,410)	(7,629)	103
Equity in earnings of equity method investments in the Managed Programs and real estate			380
Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance - beginning of period	37,650	13,597	(7,488)
Reconciliation Of Accumulated Comprehensive Income [Abstract]
Other comprehensive income (loss) before reclassifications	16,582	29,391	17,911
Amounts reclassified from accumulated other comprehensive income (loss) to:
Amount reclassified from accumulated other comprehensive income (loss)	(7,304)	(5,338)	3,174
Net current period other comprehensive income (loss)	9,278	24,053	21,085
Net current period other comprehensive loss attributable to noncontrolling interests and redeemable noncontrolling interest	7	0	0
Balance - end of period	46,935	37,650	13,597
Gains and Losses on Derivative Instruments | Amounts reclassified from accumulated other comprehensive income (loss) to:
Amounts reclassified from accumulated other comprehensive income (loss) to:
Interest expense	2,106	2,291	2,691
Other income and (expenses)	(9,410)	(7,629)	103
Equity in earnings of equity method investments in the Managed Programs and real estate			380
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance - beginning of period	(209,977)	(89,177)	22,793
Reconciliation Of Accumulated Comprehensive Income [Abstract]
Other comprehensive income (loss) before reclassifications	(92,434)	(125,447)	(117,938)
Amounts reclassified from accumulated other comprehensive income (loss) to:
Amount reclassified from accumulated other comprehensive income (loss)	0	0	0
Net current period other comprehensive income (loss)	(92,434)	(125,447)	(117,938)
Net current period other comprehensive loss attributable to noncontrolling interests and redeemable noncontrolling interest	1,081	4,647	5,968
Balance - end of period	(301,330)	(209,977)	(89,177)
Foreign Currency Translation Adjustments | Amounts reclassified from accumulated other comprehensive income (loss) to:
Amounts reclassified from accumulated other comprehensive income (loss) to:
Interest expense	0	0	0
Other income and (expenses)	0	0	0
Equity in earnings of equity method investments in the Managed Programs and real estate			0
Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance - beginning of period	36	21	31
Reconciliation Of Accumulated Comprehensive Income [Abstract]
Other comprehensive income (loss) before reclassifications	(126)	15	(10)
Amounts reclassified from accumulated other comprehensive income (loss) to:
Amount reclassified from accumulated other comprehensive income (loss)	0	0	0
Net current period other comprehensive income (loss)	(126)	15	(10)
Net current period other comprehensive loss attributable to noncontrolling interests and redeemable noncontrolling interest	0	0	0
Balance - end of period	(90)	36	21
Gains and Losses on Marketable Securities | Amounts reclassified from accumulated other comprehensive income (loss) to:
Amounts reclassified from accumulated other comprehensive income (loss) to:
Interest expense	0	0	0
Other income and (expenses)	$ 0	$ 0	0
Equity in earnings of equity method investments in the Managed Programs and real estate			$ 0