Debt - Narrative (Details)	6 Months Ended
	Jun. 30, 2018 USD ($) extension instrument	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Number of lines of unsecured credit (in instruments) | instrument	2
Unsecured Debt [Member]
Debt Instrument [Line Items]
Unamortized discount (premium), net	$ 6,800,000	$ 5,200,000
Unamortized debt issuance expense	20,100,000	18,100,000
Line of Credit [Member]
Debt Instrument [Line Items]
Aggregate borrowing capacity	1,240,000,000
Line of Credit [Member] | Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Unamortized debt issuance expense	4,600,000	3,200,000
Unsecured Line of Credit [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Aggregate borrowing capacity	$ 1,200,000,000
Number of extension options (in extensions) | extension	1
Extension period (in months)	18 months
Unsecured Line of Credit [Member] | Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	0.875%
Unsecured Line of Credit [Member] | Line of Credit Working Capital [Member]
Debt Instrument [Line Items]
Aggregate borrowing capacity	$ 35,000,000
Unsecured Line of Credit [Member] | Line of Credit Working Capital [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	0.875%
Mortgage notes payable, net [Member]
Debt Instrument [Line Items]
Unamortized discount (premium), net	$ (25,200,000)	(33,200,000)
Unamortized debt issuance expense	$ 4,500,000	$ 5,400,000