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Risk Management and Use of Derivative Financial Instruments - Narratives (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Concentration Risk
Collateral posted for derivative positions	$ 0		$ 0		$ 0
Interest expense	16,578,000	$ 16,488,000	32,987,000	$ 33,269,000
Estimated amount of derivative income to be reclassified from OCI to income			200,000
Total credit exposure on derivatives (less than)	100,000		100,000
Derivatives in net liability position, fair value	0		0		$ 0
Individual Counterparty
Concentration Risk
Total credit exposure on derivatives (less than)	100,000		100,000
AOCI Including Portion Attributable to Noncontrolling Interest
Concentration Risk
Unrealized gain (loss) on derivative instruments	(27,000)	(102,000)	(178,000)	45,000
AOCI Including Portion Attributable to Noncontrolling Interest \| Amounts reclassified from accumulated other comprehensive income
Concentration Risk
Interest expense	$ 17,000	$ 212,000	$ 43,000	$ 380,000