RESIDENTIAL MORTGAGE INVESTMENTS - Schedule of Residential Mortgage Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	$ 12,866,802		$ 12,832,514
Investment Premiums	420,268		417,912
Amortized Cost Basis	13,287,070		13,250,426
Carrying Amount	13,529,211	[1]	13,475,874	[1]
Net WAC (in hundredths)	2.58%	[2]	2.59%	[2]
Average Yield (in hundredths)	1.79%	[2]	1.74%	[2]
Agency Securities [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	12,858,164		12,823,417
Investment Premiums	420,213		417,854
Amortized Cost Basis	13,278,377		13,241,271
Carrying Amount	13,520,518	[1]	13,466,719	[1]
Net WAC (in hundredths)	2.57%	[2]	2.59%	[2]
Average Yield (in hundredths)	1.79%	[2]	1.74%	[2]
Agency Securities [Member] | Fixed-Rate [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	2,089		2,158
Investment Premiums	5		6
Amortized Cost Basis	2,094		2,164
Carrying Amount	2,096	[1]	2,167	[1]
Net WAC (in hundredths)	6.65%	[2]	6.47%	[2]
Average Yield (in hundredths)	6.55%	[2]	6.47%	[2]
Agency Securities [Member] | ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	10,726,961		10,675,620
Investment Premiums	346,807		343,452
Amortized Cost Basis	11,073,768		11,019,072
Carrying Amount	11,300,859	[1]	11,231,057	[1]
Net WAC (in hundredths)	2.56%	[2]	2.58%	[2]
Average Yield (in hundredths)	1.83%	[2]	1.76%	[2]
Agency Securities [Member] | Ginnie Mae ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	2,129,114		2,145,639
Investment Premiums	73,401		74,396
Amortized Cost Basis	2,202,515		2,220,035
Carrying Amount	2,217,563	[1]	2,233,495	[1]
Net WAC (in hundredths)	2.62%	[2]	2.64%	[2]
Average Yield (in hundredths)	1.60%	[2]	1.64%	[2]
Residential Mortgage Loans [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	6,451		6,877
Investment Premiums	19		21
Amortized Cost Basis	6,470		6,898
Carrying Amount	6,470	[1]	6,898	[1]
Net WAC (in hundredths)	4.96%	[2]	5.03%	[2]
Average Yield (in hundredths)	4.10%	[2]	4.20%	[2]
Residential Mortgage Loans [Member] | Fixed-Rate [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	2,315		2,633
Investment Premiums	2		3
Amortized Cost Basis	2,317		2,636
Carrying Amount	2,317	[1]	2,636	[1]
Net WAC (in hundredths)	7.01%	[2]	6.99%	[2]
Average Yield (in hundredths)	5.39%	[2]	5.63%	[2]
Residential Mortgage Loans [Member] | ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	4,136		4,244
Investment Premiums	17		18
Amortized Cost Basis	4,153		4,262
Carrying Amount	4,153	[1]	4,262	[1]
Net WAC (in hundredths)	3.82%	[2]	3.81%	[2]
Average Yield (in hundredths)	3.31%	[2]	3.35%	[2]
Collateral For Structured Financings [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Unpaid Principal Balance	2,187		2,220
Investment Premiums	36		37
Amortized Cost Basis	2,223		2,257
Carrying Amount	$ 2,223	[1]	$ 2,257	[1]
Net WAC (in hundredths)	8.09%	[2]	8.09%	[2]
Average Yield (in hundredths)	7.61%	[2]	7.68%	[2]

[1] Includes unrealized gains and losses for residential mortgage investments classified as available-for-sale (see NOTE 10).

[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 quarter 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.