Commercial Mortgage Residual Interests Securitizations (Details) - securitizations	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Number of securitizations	4	4	7
Remaining number of securitizations	3	3