Consolidated Variable Interest Entities Consolidated Variable Interest Entities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Payments to Acquire Additional Interest in Subsidiaries	$ 100
Investment property, net	5,645,354	$ 5,469,481
Other assets	134,304	146,450
Variable Interest Entity, Consolidated, Carrying Amount, Assets	51,852	92,041
Secured debt	2,867,356	2,819,567
Other liabilities	270,741	279,667
Consolidated variable interest entities	4,285	(2,982)
Variable Interest Entities, Consolidated, Total Liabilities and Stockholder's Equity	$ 47,723	61,127
VIE Percent of Consolidated Assets	0.80%
VIE Percent of Consolidated Liabilities	1.20%
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investment property, net	$ 50,193	88,987
Other assets	1,659	3,054
Secured debt	41,970	62,111
Other liabilities	$ 1,468	$ 1,998