Real Estate Investments - Unconsolidated Joint Ventures Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) property joint_venture	Dec. 31, 2015 USD ($) property joint_venture	Dec. 31, 2014 USD ($) property
Schedule of Equity Method Investments [Line Items]
Aggregate equity investments	$ 46,077,000	$ 56,824,000
Net (loss) income	$ (415,000)	2,361,000	$ (77,000)
Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties owned | property	619
Aggregate balance outstanding	$ 2,629,949,000	3,039,882,000
Unconsolidated Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Aggregate equity investments	41,300,000	52,800,000
Net (loss) income	900,000	$ 2,300,000	$ 1,500,000
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	3
Number of properties owned | property	2	3	6