Debt - Schedule of Debt (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) note_payable
Debt [Roll Forward]
Total debt, Beginning balance	$ 6,073,444
Debt Issuances, Net	380,089
Repayments, Extinguishment and Assumptions, Net	(447,672)
Accretion and Amortization	2,633
Total debt, Ending balance	6,008,494
Mortgage Notes Payable and Other Debt [Member]
Debt [Roll Forward]
Total debt, Beginning balance	2,082,692
Debt Issuances, Net	89
Repayments, Extinguishment and Assumptions, Net	(2,672)
Accretion and Amortization	(1,516)
Total debt, Ending balance	2,078,593
Mortgages [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	2,071,038
Net premiums (discount), Beginning balance	24,652
Deferred costs, Beginning balance	(12,998)
Debt Issuances	89
Repayments, Extinguishment and Assumptions	(2,672)
Accretion and Amortization, (Premiums) Discount	(2,123)
Accretion and Amortization, Deferred costs	607
Outstanding balance, Ending balance	2,068,455
Net premiums (discount), Ending balance	22,529
Deferred costs, Ending balance	(12,391)
Mortgage notes in connection with default from non-recourse loan	$ 16,200
Number of mortgage notes payable in default | note_payable	1
Corporate Bonds [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	$ 2,850,000
Net premiums (discount), Beginning balance	(1,232)
Deferred costs, Beginning balance	(27,274)
Total debt, Beginning balance	2,821,494
Accretion and Amortization, (Premiums) Discount	176
Accretion and Amortization, Deferred costs	1,160
Accretion and Amortization	1,336
Outstanding balance, Ending balance	2,850,000
Net premiums (discount), Ending balance	(1,056)
Deferred costs, Ending balance	(26,114)
Total debt, Ending balance	2,822,830
Convertible Debt [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	1,000,000
Net premiums (discount), Beginning balance	(7,782)
Deferred costs, Beginning balance	(7,960)
Total debt, Beginning balance	984,258
Accretion and Amortization, (Premiums) Discount	1,317
Accretion and Amortization, Deferred costs	1,496
Accretion and Amortization	2,813
Outstanding balance, Ending balance	1,000,000
Net premiums (discount), Ending balance	(6,465)
Deferred costs, Ending balance	(6,464)
Total debt, Ending balance	987,071
Credit Facility [Member]
Debt [Roll Forward]
Total debt, Beginning balance	185,000
Debt Issuances, Net	380,000
Repayments, Extinguishment and Assumptions, Net	(445,000)
Accretion and Amortization	0
Total debt, Ending balance	$ 120,000