Debt - Revolving and Term Credit Facilities (Details)	Jan. 23, 2015 USD ($) option	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Unsecured revolving credit facility		$ 20,000,000	$ 0
Secured Revolving and Term Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Write off of deferred debt issuance cost	$ 1,300,000
Unsecured revolving credit facility			470,000,000
Unsecured Revolving Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Current borrowing capacity	800,000,000
Maximum borrowing capacity	$ 1,250,000,000.00
Unsecured revolving credit facility		$ 20,000,000	$ 0
Option to extend maturity, number | option	2
Extension period	6 months
Extension fee percent of outstanding commitments under revolving credit facility	0.075%
Maximum leverage ratio	60.00%
Maximum consolidated secured indebtedness to asset value	40.00%
Minimum tangible net worth	$ 745,400,000.0
Tangible net worth. minimum percent of net equity proceeds received	75.00%
Minimum adjusted EBITDA to consolidated fixed charges	1.50
Minimum net operating income to unsecured debt	1.75
Maximum ratio of unsecured debt to unencumbered asset value	60.00%
Maximum consolidated secured recourse debt to asset value	10.00%
Unsecured Revolving Credit Facility | Revolving Credit Facility | Eurodollar | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.875%
Unsecured Revolving Credit Facility | Revolving Credit Facility | Eurodollar | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.60%
Unsecured Revolving Credit Facility | Revolving Credit Facility | Base Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Unsecured Revolving Credit Facility | Revolving Credit Facility | Base Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.60%