Real Estate Investments - Unconsolidated Joint Ventures Narrative (Details)	3 Months Ended
	Mar. 31, 2017 USD ($) property joint_venture	Mar. 31, 2016 USD ($) property	Dec. 31, 2016 USD ($) property joint_venture
Schedule of Equity Method Investments [Line Items]
Aggregate equity investments	$ 45,145,000		$ 46,077,000
Net (loss) income	$ (82,000)	$ 206,000
Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties owned | property	597
Aggregate balance outstanding	$ 2,553,386,000		2,629,949,000
Unconsolidated Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Aggregate equity investments	41,000,000		$ 41,300,000
Net (loss) income	300,000	$ 300,000
Unconsolidated Joint Venture [Member] | Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Aggregate balance outstanding	20,400,000
Unconsolidated Joint Venture [Member] | Mortgages [Member] | Recourse debt [Member]
Schedule of Equity Method Investments [Line Items]
Aggregate balance outstanding	$ 0
Unconsolidated Properties [Member] | REI segment [Member]
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated joint ventures | joint_venture	2		2
Number of properties owned | property	2	2	2