RESIDENTIAL MORTGAGE INVESTMENTS - Schedule of Residential Mortgage Investments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	$ 13,222,629		$ 12,832,514
Investment Premiums	432,744		417,912
Amortized Cost Basis	13,655,373		13,250,426
Carrying Amount	13,908,104	[1]	13,475,874	[1]
Net WAC (in hundredths)	2.54%	[2]	2.59%	[2]
Average Yield (in hundredths)	1.69%	[2]	1.59%	[2]
Agency Securities [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	13,215,738		12,823,417
Investment Premiums	432,696		417,854
Amortized Cost Basis	13,648,434		13,241,271
Carrying Amount	13,901,165	[1]	13,466,719	[1]
Net WAC (in hundredths)	2.54%	[2]	2.59%	[2]
Average Yield (in hundredths)	1.69%	[2]	1.59%	[2]
Agency Securities [Member] | Fixed-Rate [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	1,660		2,158
Investment Premiums	4		6
Amortized Cost Basis	1,664		2,164
Carrying Amount	1,665	[1]	2,167	[1]
Net WAC (in hundredths)	6.63%	[2]	6.67%	[2]
Average Yield (in hundredths)	6.45%	[2]	6.40%	[2]
Agency Securities [Member] | ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	10,230,419		10,675,620
Investment Premiums	328,781		343,452
Amortized Cost Basis	10,559,200		11,019,072
Carrying Amount	10,800,332	[1]	11,231,057	[1]
Net WAC (in hundredths)	2.51%	[2]	2.58%	[2]
Average Yield (in hundredths)	1.72%	[2]	1.59%	[2]
Agency Securities [Member] | Ginnie Mae ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	2,983,659		2,145,639
Investment Premiums	103,911		74,396
Amortized Cost Basis	3,087,570		2,220,035
Carrying Amount	3,099,168	[1]	2,233,495	[1]
Net WAC (in hundredths)	2.63%	[2]	2.64%	[2]
Average Yield (in hundredths)	1.53%	[2]	1.57%	[2]
Residential Mortgage Loans [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	4,894		6,877
Investment Premiums	15		21
Amortized Cost Basis	4,909		6,898
Carrying Amount	4,909	[1]	6,898	[1]
Net WAC (in hundredths)	4.95%	[2]	5.03%	[2]
Average Yield (in hundredths)	3.97%	[2]	4.27%	[2]
Residential Mortgage Loans [Member] | Fixed-Rate [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	1,848		2,633
Investment Premiums	2		3
Amortized Cost Basis	1,850		2,636
Carrying Amount	1,850	[1]	2,636	[1]
Net WAC (in hundredths)	6.96%	[2]	6.99%	[2]
Average Yield (in hundredths)	5.46%	[2]	5.62%	[2]
Residential Mortgage Loans [Member] | ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	3,046		4,244
Investment Premiums	13		18
Amortized Cost Basis	3,059		4,262
Carrying Amount	3,059	[1]	4,262	[1]
Net WAC (in hundredths)	3.73%	[2]	3.81%	[2]
Average Yield (in hundredths)	3.14%	[2]	3.46%	[2]
Collateral For Structured Financings [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	1,997		2,220
Investment Premiums	33		37
Amortized Cost Basis	2,030		2,257
Carrying Amount	$ 2,030	[1]	$ 2,257	[1]
Net WAC (in hundredths)	8.11%	[2]	8.09%	[2]
Average Yield (in hundredths)	7.62%	[2]	7.34%	[2]

[1] Includes unrealized gains and losses for residential mortgage investments classified as available-for-sale (see NOTE 9).

[2] Net WAC, or weighted average coupon, is the weighted average interest rate of the mortgage loans underlying the indicated investments net of servicing and other fees as of the indicated balance sheet date. Net WAC is expressed as a percentage calculated on an annualized basis on the unpaid principal balances of the mortgage loans underlying these investments. Average yield is presented for the year then ended, and is based on the cash component of interest income expressed as a percentage calculated on an annualized basis on average amortized cost basis (the "cash yield") less the effects of amortizing investment premiums. Investment premium amortization is determined using the interest method and incorporates actual and anticipated future mortgage prepayments.