Variable Interest Entities (Narrative) (Details) $ in Thousands		6 Months Ended	9 Months Ended	12 Months Ended
		Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) property joint_venture	Dec. 31, 2016 USD ($) property joint_venture
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures guaranteed by company | joint_venture			1	1
Acquired property net book value	[1]		$ 210,184	$ 476,117
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures | joint_venture			9	9
Number of real estate properties | property			22	25
Acquired property net book value				$ 249,500
Variable interest entity, consolidated, additional contributions made			$ 100	$ 2,500
Unconsolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures | joint_venture			2	2
Variable interest entity, nonconsolidated, additional future funding			$ 99,000
Scenario, Forecast [Member] | Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Variable interest entity, consolidated, additional contributions made		$ 100

[1] Consolidated variable interest entities' assets and debt included in the above balances (see Note 15) at September 30, 2017 and December 31, 2016 are Property, net of $210,184 and $476,117; Accrued Rent and Accounts Receivable, net of $11,385 and $11,066; Cash and Cash Equivalents of $8,457 and $9,560; Debt, net of $46,473 and $47,112.