Debt And Lines Of Credit , Schedule of debt and lines of credit (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Secured debt	$ 2,832,819	$ 2,819,567
Debt weighted average to maturity, years	8 years 8 months 12 days	8 years 6 months
Weighted average interest rate	4.60%	4.50%
Lines of credit		$ 100,095
Total debt	$ 3,018,653	3,110,042
Collateralized term loans - CMBS [Member]
Debt Instrument [Line Items]
Secured debt	$ 1,034,261	$ 492,294
Debt weighted average to maturity, years	6 years 1 month 6 days	5 years 7 months 6 days
Weighted average interest rate	4.40%	5.20%
Preferred OP units [Member]
Debt Instrument [Line Items]
Secured debt	$ 45,903	$ 45,903
Debt weighted average to maturity, years	15 years 7 months 6 days	5 years 4 months 24 days
Weighted average interest rate	10.00%	6.90%
Line of Credit [Member]
Debt Instrument [Line Items]
Lines of credit		$ 100,300
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Debt Instrument [Line Items]
Secured debt	$ 389,076	$ 1,046,803
Debt weighted average to maturity, years	7 years 4 months 24 days	6 years 7 months 6 days
Weighted average interest rate	3.90%	4.30%
Life Companies [Member] | Collateralized Mortgage Backed Securities [Member]
Debt Instrument [Line Items]
Secured debt	$ 955,251	$ 888,705
Debt weighted average to maturity, years	12 years 8 months 12 days	12 years 2 months 12 days
Weighted average interest rate	3.90%	3.90%
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Debt Instrument [Line Items]
Secured debt	$ 454,231	$ 391,765
Debt weighted average to maturity, years	5 years 6 months	7 years 10 months 24 days
Weighted average interest rate	5.10%	3.90%
Carrying Value [Member] | Secured borrowing [Member]
Debt Instrument [Line Items]
Secured debt	$ 139,496	$ 144,477
Debt weighted average to maturity, years	5 years	15 years 8 months 12 days
Weighted average interest rate	6.90%	10.00%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Lines of credit	$ 435	$ 100,095
Revolving Credit Facility [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Debt weighted average to maturity, years	1 year	3 years 7 months 6 days
Weighted average interest rate	0.00%	2.10%