Debt - Schedule of Debt (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Debt [Roll Forward]
Total debt, Beginning balance	$ 6,087,922
Debt Issuances, Net	894,732
Repayments, Extinguishment and Assumptions, Net	(959,426)
Accretion and Amortization	1,102
Total debt, Ending balance	6,024,330
Mortgages [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	1,917,132
Net premiums (discount), Beginning balance	16,077
Deferred costs, Beginning balance	(10,552)
Total debt, Beginning balance	1,922,657
Repayments, Extinguishment and Assumptions	(2,426)
Repayments, Extinguishment and Assumptions, Net	(2,426)
Accretion and Amortization, (Premiums) Discount	(2,006)
Accretion and Amortization, Deferred costs	601
Accretion and Amortization	(1,405)
Outstanding balance, Ending balance	1,914,706
Net premiums (discount), Ending balance	14,071
Deferred costs, Ending balance	(9,951)
Total debt, Ending balance	1,918,826
Corporate Bonds [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	3,400,000
Net premiums (discount), Beginning balance	(4,115)
Deferred costs, Beginning balance	(27,276)
Total debt, Beginning balance	3,368,609
Repayments, Extinguishment and Assumptions	(750,000)
Repayments, Extinguishment and Assumptions, Net	(750,000)
Accretion and Amortization, (Premiums) Discount	194
Accretion and Amortization, Deferred costs	1,153
Accretion and Amortization	1,347
Outstanding balance, Ending balance	2,650,000
Net premiums (discount), Ending balance	(3,921)
Deferred costs, Ending balance	(26,123)
Total debt, Ending balance	2,619,956
Convertible Debt [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	402,500
Net premiums (discount), Beginning balance	(3,909)
Deferred costs, Beginning balance	(3,708)
Total debt, Beginning balance	394,883
Accretion and Amortization, (Premiums) Discount	485
Accretion and Amortization, Deferred costs	455
Accretion and Amortization	940
Outstanding balance, Ending balance	402,500
Net premiums (discount), Ending balance	(3,424)
Deferred costs, Ending balance	(3,253)
Total debt, Ending balance	395,823
Credit Facility [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	403,000
Deferred costs, Beginning balance	(1,227)
Total debt, Beginning balance	401,773
Debt Issuances	899,000
Debt Issuances, Deferred costs	(4,268)
Debt Issuances, Net	894,732
Repayments, Extinguishment and Assumptions	(207,000)
Repayments, Extinguishment and Assumptions, Net	(207,000)
Accretion and Amortization, Deferred costs	220
Accretion and Amortization	220
Outstanding balance, Ending balance	1,095,000
Deferred costs, Ending balance	(5,275)
Total debt, Ending balance	$ 1,089,725