Debt - Schedule of Debt (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Debt [Roll Forward]
Total debt, Beginning balance	$ 6,073,444
Debt Issuances, Net	1,558,139
Repayments, Extinguishment and Assumptions, Net	(1,689,253)
Accretion and Amortization	6,758
Total debt, Ending balance	5,949,088
Mortgage Notes Payable and Other Debt [Member]
Debt [Roll Forward]
Total debt, Beginning balance	2,082,692
Debt Issuances, Net	139
Repayments, Extinguishment and Assumptions, Net	(141,753)
Accretion and Amortization	(4,492)
Total debt, Ending balance	1,936,586
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	182
Debt Issuances, Deferred costs	(43)
Repayments, Extinguishment and Assumptions	(141,613)
Repayments, Extinguishment and Assumptions of Debt, Premium, Amount	(169)
Repayments, Extinguishment and Assumptions of Debt, Deferred Costs, Amount	29
Accretion and Amortization, (Premiums) Discount	(6,341)
Accretion and Amortization, Deferred costs	1,849
Outstanding balance, Ending balance	1,929,607
Net premiums (discount), Ending balance	18,142
Deferred costs, Ending balance	(11,163)
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	538
Accretion and Amortization, Deferred costs	3,509
Accretion and Amortization	4,047
Outstanding balance, Ending balance	2,850,000
Net premiums (discount), Ending balance	(694)
Deferred costs, Ending balance	(23,765)
Total debt, Ending balance	2,825,541
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
Repayments, Extinguishment and Assumptions	(597,500)
Repayments, Extinguishment and Assumptions, Net	(597,500)
Accretion and Amortization, (Premiums) Discount	3,400
Accretion and Amortization, Deferred costs	3,803
Accretion and Amortization	7,203
Outstanding balance, Ending balance	402,500
Net premiums (discount), Ending balance	(4,382)
Deferred costs, Ending balance	(4,157)
Total debt, Ending balance	393,961
Credit Facility [Member]
Debt [Roll Forward]
Total debt, Beginning balance	185,000
Debt Issuances, Net	1,558,000
Repayments, Extinguishment and Assumptions, Net	(950,000)
Accretion and Amortization	0
Total debt, Ending balance	$ 793,000