Equity - Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss)
Beginning equity balance, value			$ 2,343,257	$ 2,315,004
Amounts reclassified from accumulated other comprehensive loss to:
Interest expense	$ 20,801	$ 21,453	41,351	44,843
Total other comprehensive (loss) income	(49,439)	40,171	(24,836)	46,257
Ending equity balance, value	2,289,312	2,353,941	2,289,312	2,353,941
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning equity balance, value	(54,364)	(150,849)	(78,420)	(156,676)
Amounts reclassified from accumulated other comprehensive loss to:
Ending equity balance, value	(102,802)	(111,800)	(102,802)	(111,800)
Gains and Losses on Derivative Instruments
Accumulated Other Comprehensive Income (Loss)
Beginning equity balance, value	6,755	26,996	9,087	29,549
Amounts reclassified from accumulated other comprehensive loss to:
Ending equity balance, value	12,120	16,857	12,120	16,857
Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss)
Beginning equity balance, value	(15)	(18)	(15)	(48)
Amounts reclassified from accumulated other comprehensive loss to:
Ending equity balance, value	(15)	(17)	(15)	(17)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss)
Beginning equity balance, value	(61,104)	(177,827)	(87,492)	(186,177)
Amounts reclassified from accumulated other comprehensive loss to:
Ending equity balance, value	(114,907)	(128,640)	(114,907)	(128,640)
AOCI Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss)
Other comprehensive loss before reclassifications	(48,451)	40,729	(22,792)	48,967
Amounts reclassified from accumulated other comprehensive loss to:
Total	(988)	(558)	(2,044)	(2,710)
Total other comprehensive (loss) income	(49,439)	40,171	(24,836)	46,257
AOCI Including Portion Attributable to Noncontrolling Interest | Reclassification out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive loss to:
Interest expense	327	603	763	1,309
Other income and (expenses)	(1,315)	(1,161)	(2,807)	(4,019)
Gains and (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss)
Other comprehensive loss before reclassifications	6,353	(9,581)	5,077	(9,982)
Amounts reclassified from accumulated other comprehensive loss to:
Total	(988)	(558)	(2,044)	(2,710)
Total other comprehensive (loss) income	5,365	(10,139)	3,033	(12,692)
Gains and (Losses) on Derivative Instruments | Reclassification out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive loss to:
Interest expense	327	603	763	1,309
Other income and (expenses)	(1,315)	(1,161)	(2,807)	(4,019)
Gains and (Losses) on Marketable Investments
Accumulated Other Comprehensive Income (Loss)
Other comprehensive loss before reclassifications	0	1	0	31
Amounts reclassified from accumulated other comprehensive loss to:
Total	0	0	0	0
Total other comprehensive (loss) income	0	1	0	31
Gains and (Losses) on Marketable Investments | Reclassification out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive loss to:
Interest expense	0	0	0	0
Other income and (expenses)	0	0	0	0
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss)
Other comprehensive loss before reclassifications	(54,804)	50,309	(27,869)	58,918
Amounts reclassified from accumulated other comprehensive loss to:
Total	0	0	0	0
Total other comprehensive (loss) income	(54,804)	50,309	(27,869)	58,918
Foreign Currency Translation Adjustments | Reclassification out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive loss to:
Interest expense	0	0	0	0
Other income and (expenses)	0	0	0	0
Noncontrolling Interests
Amounts reclassified from accumulated other comprehensive loss to:
Net current-period Other comprehensive income attributable to noncontrolling interests	1,001	(1,122)	454	(1,381)
Gains and Losses on Derivative Instruments
Amounts reclassified from accumulated other comprehensive loss to:
Net current-period Other comprehensive income attributable to noncontrolling interests	0	0	0	0
Gains and Losses on Marketable Securities
Amounts reclassified from accumulated other comprehensive loss to:
Net current-period Other comprehensive income attributable to noncontrolling interests	0	0	0	0
Foreign Currency Translation Adjustments
Amounts reclassified from accumulated other comprehensive loss to:
Net current-period Other comprehensive income attributable to noncontrolling interests	$ 1,001	$ (1,122)	$ 454	$ (1,381)