Summary of Significant Accounting Policies - Schedule of Material Changes Between Cash Flow Classifications due to Substantial Debt Prepayment Penalties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Amortization of discounts and premiums on debt	$ 3,536	$ (17,986)	$ (10,569)
Net (gain) loss on debt extinguishment	12,258	114,666	0
Net cash provided by operating activities	1,265,788	1,214,123	1,356,628
CASH FLOWS FROM INVESTING ACTIVITIES:
Net cash provided by investing activities	(594,296)	5,903,942	(695,814)
CASH FLOWS FROM FINANCING ACTIVITIES:
Commercial paper proceeds	5,066,509	1,760,194	3,932,304
Net cash (used for) financing activities	(789,818)	(7,054,092)	(666,167)
Cash and cash equivalents, beginning of year	77,207	42,276
Cash and cash equivalents and restricted deposits, beginning of year	219,088	155,115	160,468
Cash and cash equivalents, end of year	50,647	77,207	42,276
Cash and cash equivalents and restricted deposits, end of year	100,762	219,088	155,115
Write-off of pursuit costs	3,106	4,092	2,878
Scenario, Previously Reported [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Amortization of discounts and premiums on debt		(17,378)	(9,492)
(Increase) decrease in deposits - restricted		11,450	(1,794)
(Increase) decrease in mortgage deposits		(26)	258
Net cash provided by operating activities		1,111,489	1,356,499
CASH FLOWS FROM INVESTING ACTIVITIES:
(Increase) decrease in deposits on real estate acquisitions and investments, net		(32,503)	17,874
(Increase) decrease in mortgage deposits		534	(531)
Net cash provided by investing activities		5,871,973	(678,471)
CASH FLOWS FROM FINANCING ACTIVITIES:
Mortgage deposits		(8,497)	(8,588)
Commercial paper proceeds		1,759,586	3,931,227
Net cash (used for) financing activities		(6,948,531)	(675,832)
Cash and cash equivalents, beginning of year	77,207	42,276	40,080
Cash and cash equivalents, end of year		77,207	42,276
Write-off of pursuit costs			3,208
Reclassification Adjustments [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Amortization of discounts and premiums on debt		(608)	(1,077)
Net (gain) loss on debt extinguishment		114,666
(Increase) decrease in deposits - restricted		(11,450)	1,794
(Increase) decrease in mortgage deposits		26	(258)
Net cash provided by operating activities		102,634	129
CASH FLOWS FROM INVESTING ACTIVITIES:
(Increase) decrease in deposits on real estate acquisitions and investments, net		32,503	(17,874)
(Increase) decrease in mortgage deposits		(534)	531
Net cash provided by investing activities		31,969	(17,343)
CASH FLOWS FROM FINANCING ACTIVITIES:
Mortgage deposits		8,497	8,588
Commercial paper proceeds		608	1,077
Net cash (used for) financing activities		(105,561)	9,665
(adjustments for restricted deposits, beginning of year)	141,881	112,839	120,388
(adjustments for restricted deposits, end of year)		141,881	112,839
Write-off of pursuit costs			(330)
Mortgage Notes Payable, Net [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Net gain (loss) on debt extinguishment		(31,732)
Mortgage Notes Payable, Net [Member] | Reclassification Adjustments [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Net gain (loss) on debt extinguishment		(31,732)
Notes, Net [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Net gain (loss) on debt extinguishment	$ 0	(82,934)	$ 0
Notes, Net [Member] | Reclassification Adjustments [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Net gain (loss) on debt extinguishment		$ (82,934)