Debt And Lines Of Credit , Table - Schedule of debt and lines of credit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Secured debt	$ 2,819,567	$ 2,125,267
Debt weighted average to maturity, years	8 years 6 months	8 years 4 months 24 days
Weighted average interest rate	4.50%	5.00%
Lines of credit	$ 100,095	$ 24,687
Collateralized Mortgage Backed Securities [Member]
Debt Instrument [Line Items]
Secured debt		2,800,000
Collateralized term loans - CMBS [Member]
Debt Instrument [Line Items]
Secured debt	$ 492,294	$ 639,321
Debt weighted average to maturity, years	5 years 7 months 6 days	5 years 3 months 18 days
Weighted average interest rate	5.20%	5.30%
Aspen and Series B-3 Preferred OP Units [Member]
Debt Instrument [Line Items]
Secured debt	$ 45,903	$ 45,903
Debt weighted average to maturity, years	5 years 4 months 24 days	6 years 1 month 6 days
Weighted average interest rate	6.90%	6.90%
Line of Credit [Member]
Debt Instrument [Line Items]
Lines of credit	$ 100,300
Secured Debt [Member]
Debt Instrument [Line Items]
Secured debt	3,110,042	$ 2,336,297
Reported Value Measurement [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Secured debt	$ 144,477	$ 140,440
Debt weighted average to maturity, years	15 years 8 months 12 days	15 years 7 months 6 days
Weighted average interest rate	10.00%	10.20%
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Debt Instrument [Line Items]
Secured debt	$ 1,046,803	$ 789,612
Debt weighted average to maturity, years	6 years 7 months 6 days	5 years 9 months 18 days
Weighted average interest rate	4.30%	4.60%
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Debt Instrument [Line Items]
Secured debt	$ 391,765	$ 196,201
Debt weighted average to maturity, years	7 years 10 months 24 days
Weighted average interest rate	3.90%	4.00%
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] | Collateralized term loans - CMBS [Member]
Debt Instrument [Line Items]
Debt weighted average to maturity, years		9 years
Life Companies [Member] | Collateralized Mortgage Backed Securities [Member]
Debt Instrument [Line Items]
Secured debt	$ 888,705	$ 500,133
Debt weighted average to maturity, years	12 years 2 months 12 days	14 years 4 months 24 days
Weighted average interest rate	3.90%	4.10%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Lines of credit	$ 100,095	$ 24,687
Revolving Credit Facility [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Debt weighted average to maturity, years	3 years 7 months 6 days	4 years 7 months 6 days
Weighted average interest rate	2.10%	1.60%