Consolidated K-Series - Condensed Statement of Operations of Consolidated K-Series (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Income Statements, Captions [Line Items]
Interest income	$ 80,866	$ 82,587	$ 84,400	$ 88,985	$ 93,124	$ 94,937	$ 95,548	$ 95,238	$ 336,838	$ 378,847	$ 291,727
Interest expense									260,651	301,010	231,178
NET INTEREST INCOME	15,991	18,292	20,303	21,601	18,809	19,320	19,883	19,825	76,187	77,837	60,549
Unrealized gain on multi-family loans and debt held in securitization trusts, net	(4,508)	(2,170)	5,418	13,628	13,871	18,115	20,019	4,926	12,368	56,931	31,495
NET INCOME	$ 4,207	$ 25,632	$ 24,631	$ 23,543	$ 41,976	$ 39,725	$ 31,779	$ 22,711	78,013	136,191	68,955
Consolidated K-Series
Condensed Income Statements, Captions [Line Items]
Interest income									257,417	301,877	228,631
Interest expense									232,971	275,916	210,229
NET INTEREST INCOME									24,446	25,961	18,402
Unrealized gain on multi-family loans and debt held in securitization trusts, net									12,368	56,931	31,495
NET INCOME									$ 36,814	$ 82,892	$ 49,897