Schedules Of Investments (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Investment Holdings [Line Items]
Fair Value	$ 9,466,128,000		$ 6,331,048,000
Fair value of securities	9,472,094,000		6,371,145,000
Fixed Income Securities [Member]
Investment Holdings [Line Items]
Face Amount	9,028,561,000		6,186,852,000
Fair Value	9,466,128,000		6,331,048,000
Percent of Investments in Securities	878.60%	[1]	917.10%	[1]
Cost	9,239,043,000		6,329,624,000
Mortgage Pass-Through Agency RMBS [Member]
Investment Holdings [Line Items]
Face Amount	8,925,617,000		6,156,908,000
Fair Value	9,372,454,000		6,310,570,000
Cost	9,148,730,000
U.S. Treasury Bills [Member]
Investment Holdings [Line Items]
Face Amount	75,000,000
Fair Value	74,999,000
Percent of Investments in Securities	7.00%	[1]
Cost	74,995,000
U.S. Treasury Bills [Member] | 0.060%, Due 2/9/2012 [Member]
Investment Holdings [Line Items]
Face Amount	75,000,000	[2]
Fair Value	74,999,000	[2]
Yield on investment	0.06%	[2]
Debt instrument, maturity date	Feb. 09, 2012	[2]
Collateralized Loan Obligation Securities [Member]
Investment Holdings [Line Items]
Face Amount	27,944,000		29,944,000
Fair Value	18,675,000		20,478,000
Percent of Investments in Securities	1.70%	[1]	3.00%	[1]
Cost	15,318,000		21,183,000
Fair value of securities	18,675,000		20,478,000
Collateralized Loan Obligation Securities [Member] | AMMC CLO V LTD [Member]
Investment Holdings [Line Items]
Face Amount	2,249,000	[3]	2,249,000	[4]
Fair Value	1,260,000	[3]	1,349,000	[4]
Collateralized Loan Obligation Securities [Member] | AMMC CLO VII, LTD [Member]
Investment Holdings [Line Items]
Face Amount	3,900,000	[3]	3,900,000	[4]
Fair Value	2,730,000	[3]	2,578,000	[4]
Collateralized Loan Obligation Securities [Member] | ARES VIR CLO, LTD [Member]
Investment Holdings [Line Items]
Face Amount	3,775,000	[3],[5]	3,775,000	[4],[5]
Fair Value	1,472,000	[3],[5]	1,623,000	[4],[5]
Collateralized Loan Obligation Securities [Member] | BALLYROCK CLO 2006-2, LTD [Member]
Investment Holdings [Line Items]
Face Amount	4,270,000	[3]	4,270,000	[4]
Fair Value	3,672,000	[3]	3,843,000	[4]
Collateralized Loan Obligation Securities [Member] | CARLYLE HIGH YIELD PARTNERS VIII, LTD [Member]
Investment Holdings [Line Items]
Face Amount	3,000,000	[3]	3,000,000	[4]
Fair Value	2,040,000	[3]	2,250,000	[4]
Collateralized Loan Obligation Securities [Member] | EATON VANCE CDO IX, LTD [Member]
Investment Holdings [Line Items]
Face Amount	2,500,000	[3]	2,500,000	[4]
Fair Value	1,675,000	[3]	1,915,000	[4]
Collateralized Loan Obligation Securities [Member] | FLAGSHIP CLO V, LTD [Member]
Investment Holdings [Line Items]
Face Amount	3,750,000	[3]	3,750,000	[4]
Fair Value	2,606,000	[3]	2,363,000	[4]
Collateralized Loan Obligation Securities [Member] | PHOENIX CLO II, LTD (Formerly AVENUE CLO V) [Member]
Investment Holdings [Line Items]
Face Amount	2,000,000	[3]	2,000,000	[4],[5]
Fair Value	1,620,000	[3]	1,127,000	[4],[5]
Collateralized Loan Obligation Securities [Member] | PRIMUS CLO I, LTD [Member]
Investment Holdings [Line Items]
Face Amount	2,500,000	[3]	2,500,000	[4]
Fair Value	1,600,000	[3]	1,750,000	[4]
Collateralized Loan Obligation Securities [Member] | TRIMARAN CLO VII, LTD [Member]
Investment Holdings [Line Items]
Face Amount			2,000,000	[4]
Fair Value			1,680,000	[4]
Interest Rate Cap Contracts [Member]
Investment Holdings [Line Items]
Face Amount	700,000,000		700,000,000
Fair Value	5,966,000		30,984,000
Percent of Investments in Securities	0.60%	[1]	4.50%	[1]
Cost	13,722,000		17,560,000
Interest Rate Cap Contracts [Member] | December 2014 Expiration, Cap Rate 2.073% [Member]
Investment Holdings [Line Items]
Face Amount	200,000,000		200,000,000
Fair Value	656,000		4,752,000
Cap Rate	2.073%		2.073%
Derivative contracts expiration date	December 2014		December 2014
Interest Rate Cap Contracts [Member] | October 2015 Expiration, Cap Rate 1.428% [Member]
Investment Holdings [Line Items]
Face Amount	300,000,000		300,000,000
Fair Value	3,062,000		15,340,000
Cap Rate	1.428%		1.428%
Derivative contracts expiration date	October 2015		October 2015
Interest Rate Cap Contracts [Member] | November 2015 Expiration, Cap Rate 1.360% [Member]
Investment Holdings [Line Items]
Face Amount	200,000,000		200,000,000
Fair Value	2,248,000		10,892,000
Cap Rate	1.36%		1.36%
Derivative contracts expiration date	November 2015		November 2015
Interest Rate Swap Contracts [Member]
Investment Holdings [Line Items]
Face Amount	4,740,000,000		3,690,000,000
Fair Value	(79,476,000)		(644,000)
Percent of Investments in Securities	7.40%	[1]	0.01%	[1]
Cost	0		0
Interest Rate Swap Contracts [Member] | May 2013 Expiration, Pay Rate 1.600%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	100,000,000		100,000,000
Fair Value	(1,266,000)		(1,496,000)
Derivative contracts expiration date	May 2013		May 2013
Interest Rate Swap Contracts, Pay Rate	1.60%		1.60%
Interest Rate Swap Contracts [Member] | June 2013 Expiration, Pay Rate 1.378%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	300,000,000		300,000,000
Fair Value	(3,000,000)		(2,718,000)
Derivative contracts expiration date	June 2013		June 2013
Interest Rate Swap Contracts, Pay Rate	1.378%		1.378%
Interest Rate Swap Contracts [Member] | July 2013 Expiration, Pay Rate 1.365%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	300,000,000		300,000,000
Fair Value	(3,034,000)		(2,484,000)
Derivative contracts expiration date	July 2013		July 2013
Interest Rate Swap Contracts, Pay Rate	1.365%		1.365%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.3088%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			400,000,000
Fair Value			(776,000)
Derivative contracts expiration date			December 2013
Interest Rate Swap Contracts, Pay Rate			1.3088%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.2813%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			500,000,000
Fair Value			(539,000)
Derivative contracts expiration date			December 2013
Interest Rate Swap Contracts, Pay Rate			1.2813%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.2640%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			400,000,000
Fair Value			(255,000)
Derivative contracts expiration date			December 2013
Interest Rate Swap Contracts, Pay Rate			1.264%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.3225%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			400,000,000
Fair Value			(904,000)
Derivative contracts expiration date			December 2013
Interest Rate Swap Contracts, Pay Rate			1.3225%
Interest Rate Swap Contracts [Member] | July 2014 Expiration, Pay Rate 1.7200%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			100,000,000
Fair Value			(733,000)
Derivative contracts expiration date			July 2014
Interest Rate Swap Contracts, Pay Rate			1.72%
Interest Rate Swap Contracts [Member] | July 2014 Expiration, Pay Rate 1.7325%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			250,000,000
Fair Value			(1,787,000)
Derivative contracts expiration date			July 2014
Interest Rate Swap Contracts, Pay Rate			1.7325%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.309%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	400,000,000
Fair Value	(4,587,000)
Derivative contracts expiration date	December 2013
Interest Rate Swap Contracts, Pay Rate	1.309%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.264%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	400,000,000
Fair Value	(4,230,000)
Derivative contracts expiration date	December 2013
Interest Rate Swap Contracts, Pay Rate	1.264%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.281%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	500,000,000
Fair Value	(5,421,000)
Derivative contracts expiration date	December 2013
Interest Rate Swap Contracts, Pay Rate	1.281%
Interest Rate Swap Contracts [Member] | December 2013 Expiration, Pay Rate 1.323%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	400,000,000
Fair Value	(4,695,000)
Derivative contracts expiration date	December 2013
Interest Rate Swap Contracts, Pay Rate	1.323%
Interest Rate Swap Contracts [Member] | July 2014 Expiration, Pay Rate 1.720%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	100,000,000
Fair Value	(2,375,000)
Derivative contracts expiration date	July 2014
Interest Rate Swap Contracts, Pay Rate	1.72%
Interest Rate Swap Contracts [Member] | July 2014 Expiration, Pay Rate 1.733%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	250,000,000
Fair Value	(6,149,000)
Derivative contracts expiration date	July 2014
Interest Rate Swap Contracts, Pay Rate	1.733%
Interest Rate Swap Contracts [Member] | August 2014 Expiration, Pay Rate 1.353%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	200,000,000		200,000,000
Fair Value	(3,059,000)		1,529,000
Derivative contracts expiration date	August 2014		August 2014
Interest Rate Swap Contracts, Pay Rate	1.353%		1.353%
Interest Rate Swap Contracts [Member] | September 2014 Expiration, Pay Rate 1.312%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	500,000,000		500,000,000
Fair Value	(7,115,000)		5,460,000
Derivative contracts expiration date	September 2014		September 2014
Interest Rate Swap Contracts, Pay Rate	1.312%		1.312%
Interest Rate Swap Contracts [Member] | October 2014 Expiration, Pay Rate 1.1725%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount			240,000,000
Fair Value			4,059,000
Derivative contracts expiration date			October 2014
Interest Rate Swap Contracts, Pay Rate			1.1725%
Interest Rate Swap Contracts [Member] | October 2014 Expiration, Pay Rate 1.173%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	240,000,000
Fair Value	(2,520,000)
Derivative contracts expiration date	October 2014
Interest Rate Swap Contracts, Pay Rate	1.173%
Interest Rate Swap Contracts [Member] | February 2015 Expiration, Pay Rate 2.145%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	500,000,000
Fair Value	(20,274,000)
Derivative contracts expiration date	February 2015
Interest Rate Swap Contracts, Pay Rate	2.145%
Interest Rate Swap Contracts [Member] | June 2016 Expiration, Pay Rate 1.940%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	300,000,000
Fair Value	(11,027,000)
Derivative contracts expiration date	June 2016
Interest Rate Swap Contracts, Pay Rate	1.94%
Interest Rate Swap Contracts [Member] | December 2016 Expiration, Pay Rate 1.426%, Receive Rate 3-Month LIBOR [Member]
Investment Holdings [Line Items]
Face Amount	250,000,000	[6]
Fair Value	(724,000)	[6]
Derivative contracts expiration date	December 2016	[6]
Interest Rate Swap Contracts, Pay Rate	1.426%	[6]
Agency Residential Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Percent of Investments in Securities	869.90%	[1]	914.10%	[1]
Cost			6,308,441,000
Fannie Mae Pools [Member]
Investment Holdings [Line Items]
Percent of Investments in Securities	785.00%	[1]	802.10%	[1]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member]
Investment Holdings [Line Items]
Face Amount	8,053,327,000		5,403,989,000
Fair Value	8,457,515,000		5,537,130,000
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.820%, Due 3/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	20,000,000	[7]
Fair Value	20,627,000	[7]
Securities, interest rate	2.82%	[7]
Debt instrument, maturity date	Mar. 01, 2042	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.840%, Due 1/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	36,000,000	[7]
Fair Value	37,288,000	[7]
Securities, interest rate	2.84%	[7]
Debt instrument, maturity date	Jan. 01, 2042	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.850%, Due 1/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	16,000,000	[7]
Fair Value	16,575,000	[7]
Securities, interest rate	2.85%	[7]
Debt instrument, maturity date	Jan. 01, 2042	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.880%, Due 12/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	63,081,000	[7]
Fair Value	65,342,000	[7]
Securities, interest rate	2.88%	[7]
Debt instrument, maturity date	Dec. 01, 2041	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.900%, Due 2/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	50,000,000	[7]
Fair Value	51,750,000	[7]
Securities, interest rate	2.90%	[7]
Debt instrument, maturity date	Feb. 01, 2042
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.940%, Due 1/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	15,000,000	[7]
Fair Value	15,572,000	[7]
Securities, interest rate	2.94%	[7]
Debt instrument, maturity date	Jan. 01, 2042	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.979%, Due 10/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	43,981,000	[7],[8]
Fair Value	45,730,000	[7],[8]
Securities, interest rate	2.979%	[7],[8]
Debt instrument, maturity date	Oct. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.005%, Due 1/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	40,986,000	[7],[8]
Fair Value	42,804,000	[7],[8]
Securities, interest rate	3.005%	[7],[8]
Debt instrument, maturity date	Jan. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.028%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	150,737,000	[7],[8]
Fair Value	157,242,000	[7],[8]
Securities, interest rate	3.028%	[7],[8]
Debt instrument, maturity date	Dec. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.054%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	48,199,000	[7],[8]
Fair Value	50,255,000	[7],[8]
Securities, interest rate	3.054%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.120%, Due 1/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	50,000,000	[7]
Fair Value	52,016,000	[7]
Securities, interest rate	3.12%	[7]
Debt instrument, maturity date	Jan. 01, 2042	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.168%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	39,736,000	[7],[8]
Fair Value	41,366,000	[7],[8]
Securities, interest rate	3.168%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.178%, Due 10/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	50,099,000	[7],[8]
Fair Value	52,153,000	[7],[8]
Securities, interest rate	3.178%	[7],[8]
Debt instrument, maturity date	Oct. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.179%, Due 7/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	36,737,000	[7],[8]
Fair Value	38,265,000	[7],[8]
Securities, interest rate	3.179%	[7],[8]
Debt instrument, maturity date	Jul. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.050%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	48,486,000	[7],[8]
Fair Value	50,252,000	[7],[8]
Securities, interest rate	3.05%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.176%, Due 1/1/2042 [Member]
Investment Holdings [Line Items]
Face Amount	36,000,000	[7]
Fair Value	37,530,000	[7]
Securities, interest rate	3.176%	[7]
Debt instrument, maturity date	Jan. 01, 2042	[7]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.000%, Due 1/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount			50,363,000	[8],[9]
Fair Value			51,416,000	[8],[9]
Securities, interest rate			3.00%	[8],[9]
Debt instrument, maturity date			Jan. 01, 2041	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.200%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	180,296,000	[7],[8]
Fair Value	187,753,000	[7],[8]
Securities, interest rate	3.20%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.214%, Due 11/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	37,557,000	[7],[8]
Fair Value	39,183,000	[7],[8]
Securities, interest rate	3.214%	[7],[8]
Debt instrument, maturity date	Nov. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.224%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	41,581,000	[7],[8]
Fair Value	43,485,000	[7],[8]
Securities, interest rate	3.224%	[7],[8]
Debt instrument, maturity date	Jul. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.238%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	110,829,000	[7],[8]
Fair Value	115,419,000	[7],[8]
Securities, interest rate	3.238%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.239%, Due 3/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	17,931,000	[7],[8]
Fair Value	18,644,000	[7],[8]
Securities, interest rate	3.239%	[7],[8]
Debt instrument, maturity date	Mar. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.246%, Due 4/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	59,124,000	[7],[8]
Fair Value	61,544,000	[7],[8]
Securities, interest rate	3.246%	[7],[8]
Debt instrument, maturity date	Apr. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.251%, Due 10/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	101,419,000	[7],[8]
Fair Value	105,830,000	[7],[8]
Securities, interest rate	3.251%	[7],[8]
Debt instrument, maturity date	Oct. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.255%, Due 11/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	42,699,000	[7],[8]
Fair Value	44,561,000	[7],[8]
Securities, interest rate	3.255%	[7],[8]
Debt instrument, maturity date	Nov. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.258%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	62,487,000	[7],[8]
Fair Value	65,219,000	[7],[8]
Securities, interest rate	3.258%	[7],[8]
Debt instrument, maturity date	Dec. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.263%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	51,090,000	[7],[8]
Fair Value	53,186,000	[7],[8]
Securities, interest rate	3.263%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.282%, Due 5/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	41,835,000	[7],[8]
Fair Value	43,569,000	[7],[8]
Securities, interest rate	3.282%	[7],[8]
Debt instrument, maturity date	May 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.284%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	89,046,000	[7],[8]
Fair Value	92,760,000	[7],[8]
Securities, interest rate	3.284%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.287%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	115,948,000	[7],[8]
Fair Value	120,770,000	[7],[8]
Securities, interest rate	3.287%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.308%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	33,112,000	[7],[8]
Fair Value	34,480,000	[7],[8]
Securities, interest rate	3.308%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.356%, Due 8/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	31,291,000	[7],[8]
Fair Value	32,620,000	[7],[8]
Securities, interest rate	3.356%	[7],[8]
Debt instrument, maturity date	Aug. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.308%, Due 10/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	145,746,000	[7],[8]
Fair Value	151,824,000	[7],[8]
Securities, interest rate	3.308%	[7],[8]
Debt instrument, maturity date	Oct. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.366%, Due 5/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	22,685,000	[7],[8]
Fair Value	23,661,000	[7],[8]
Securities, interest rate	3.366%	[7],[8]
Debt instrument, maturity date	May 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.387%, Due 4/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	52,425,000	[7],[8]
Fair Value	54,583,000	[7],[8]
Securities, interest rate	3.387%	[7],[8]
Debt instrument, maturity date	Apr. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.391%, Due 4/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	46,394,000	[7],[8]
Fair Value	48,322,000	[7],[8]
Securities, interest rate	3.391%	[7],[8]
Debt instrument, maturity date	Apr. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.396%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	109,987,000	[7],[8]
Fair Value	114,549,000	[7],[8]
Securities, interest rate	3.396%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 7/1/2021 [Member]
Investment Holdings [Line Items]
Face Amount	272,115,000	[8]
Fair Value	284,948,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Jul. 01, 2021	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 1/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	136,763,000	[8]
Fair Value	143,146,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Jan. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 2/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	92,404,000	[8]
Fair Value	96,716,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Feb. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 2/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	136,020,000	[8]
Fair Value	142,369,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Feb. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 2/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	223,866,000	[8]
Fair Value	234,314,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Feb. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	87,810,000	[8]
Fair Value	91,908,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	46,463,000	[8]
Fair Value	48,631,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 5/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	93,816,000	[8]
Fair Value	98,194,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	May 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 6/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	37,422,000	[8]
Fair Value	39,168,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Jun. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 8/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	56,102,000	[8]
Fair Value	58,720,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Aug. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.013%, Due 10/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			59,284,000	[8],[9]
Fair Value			60,418,000	[8],[9]
Securities, interest rate			3.013%	[8],[9]
Debt instrument, maturity date			Oct. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 10/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	236,583,000	[8]
Fair Value	247,625,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Oct. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.042%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			194,331,000	[9]
Fair Value			199,189,000	[9]
Securities, interest rate			3.042%	[9]
Debt instrument, maturity date			Dec. 01, 2040	[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 11/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	65,628,000	[8]
Fair Value	68,691,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Nov. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 12/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	100,000,000	[8]
Fair Value	104,667,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Dec. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 12/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	163,671,000
Fair Value	171,310,000
Securities, interest rate	3.50%
Debt instrument, maturity date	Dec. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 1/1/2027 [Member]
Investment Holdings [Line Items]
Face Amount	225,000,000
Fair Value	235,266,000
Securities, interest rate	3.50%
Debt instrument, maturity date	Jan. 01, 2027
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.546%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	37,780,000	[7],[8]
Fair Value	39,569,000	[7],[8]
Securities, interest rate	3.546%	[7],[8]
Debt instrument, maturity date	Aug. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.564%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	13,746,000	[7],[8]
Fair Value	14,405,000	[7],[8]
Securities, interest rate	3.564%	[7],[8]
Debt instrument, maturity date	Jul. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.574%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	16,592,000	[7],[8]
Fair Value	17,388,000	[7],[8]
Securities, interest rate	3.574%	[7],[8]
Debt instrument, maturity date	Jul. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.577%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	37,002,000	[7],[8]
Fair Value	38,791,000	[7],[8]
Securities, interest rate	3.577%	[7],[8]
Debt instrument, maturity date	Aug. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.599%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	64,248,000	[7],[8]
Fair Value	67,400,000	[7],[8]
Securities, interest rate	3.599%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.616%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	62,636,000	[7],[8]
Fair Value	65,703,000	[7],[8]
Securities, interest rate	3.616%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.677%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	39,283,000	[7],[8]
Fair Value	41,115,000	[7],[8]
Securities, interest rate	3.677%	[7],[8]
Debt instrument, maturity date	Jul. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.682%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	37,852,000	[7],[8]
Fair Value	39,770,000	[7],[8]
Securities, interest rate	3.682%	[7],[8]
Debt instrument, maturity date	Aug. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.699%, Due 5/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	31,975,000	[7],[8]
Fair Value	33,665,000	[7],[8]
Securities, interest rate	3.699%	[7],[8]
Debt instrument, maturity date	May 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.701%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	9,420,000	[7],[8]
Fair Value	9,902,000	[7],[8]
Securities, interest rate	3.701%	[7],[8]
Debt instrument, maturity date	Aug. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.734%, Due 9/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount	25,442,000	[7],[8]
Fair Value	26,734,000	[7],[8]
Securities, interest rate	3.734%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2039	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.210%, Due 11/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			49,731,000	[8],[9]
Fair Value			50,957,000	[8],[9]
Securities, interest rate			3.21%	[8],[9]
Debt instrument, maturity date			Nov. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.811%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	33,941,000	[7],[8]
Fair Value	35,739,000	[7],[8]
Securities, interest rate	3.811%	[7],[8]
Debt instrument, maturity date	Jul. 01, 2040	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.951%, Due 9/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount	14,578,000	[7],[8]
Fair Value	15,410,000	[7],[8]
Securities, interest rate	3.951%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2039	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.965%, Due 10/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount	30,165,000	[7],[8]
Fair Value	31,831,000	[7],[8]
Securities, interest rate	3.965%	[7],[8]
Debt instrument, maturity date	Oct. 01, 2039	[7],[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	24,558,000	[8]
Fair Value	25,938,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	181,849,000	[8]
Fair Value	192,073,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	39,570,000	[8]
Fair Value	41,795,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	43,432,000	[8]
Fair Value	45,874,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	92,625,000	[8]
Fair Value	97,833,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	7,679,000	[8]
Fair Value	8,111,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	68,350,000	[8]
Fair Value	72,193,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	138,592,000	[8]
Fair Value	146,384,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	147,502,000	[8]
Fair Value	155,795,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 5/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	43,889,000	[8]
Fair Value	46,357,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	May 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 5/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	24,805,000	[8]
Fair Value	26,200,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	May 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 5/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	172,581,000	[8]
Fair Value	182,284,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	May 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.212%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			100,076,000	[8],[9]
Fair Value			103,078,000	[8],[9]
Securities, interest rate			3.212%	[8],[9]
Debt instrument, maturity date			Dec. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 6/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	23,666,000	[8]
Fair Value	24,996,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Jun. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 6/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	94,372,000	[8]
Fair Value	99,678,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Jun. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 6/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	91,989,000	[8]
Fair Value	97,161,000	[8]
Securities, interest rate	4.00%	[8]
Debt instrument, maturity date	Jun. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 5/1/2023 [Member]
Investment Holdings [Line Items]
Face Amount	15,938,000	[8]
Fair Value	17,006,000	[8]
Securities, interest rate	4.50%	[8]
Debt instrument, maturity date	May 01, 2023	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 3/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	8,901,000	[8]
Fair Value	9,492,000	[8]
Securities, interest rate	4.50%	[8]
Debt instrument, maturity date	Mar. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 8/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	11,106,000	[8]
Fair Value	11,844,000	[8]
Securities, interest rate	4.50%	[8]
Debt instrument, maturity date	Aug. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 3/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	37,608,000	[8]
Fair Value	40,104,000	[8]
Securities, interest rate	4.50%	[8]
Debt instrument, maturity date	Mar. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 4/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	25,733,000	[8]
Fair Value	27,441,000	[8]
Securities, interest rate	4.50%	[8]
Debt instrument, maturity date	Apr. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	56,303,000	[8]
Fair Value	60,076,000	[8]
Securities, interest rate	4.50%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 5.000%, Due 4/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	155,126,000	[8]
Fair Value	167,663,000	[8]
Securities, interest rate	5.00%	[8]
Debt instrument, maturity date	Apr. 01, 2041	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 5.000%, Due 5/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	84,621,000	[8]
Fair Value	91,460,000	[8]
Securities, interest rate	5.00%	[8]
Debt instrument, maturity date	May 01, 2041	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.233%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			47,318,000	[8],[9]
Fair Value			48,667,000	[8],[9]
Securities, interest rate			3.233%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.251%, Due 11/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			49,712,000	[8],[9]
Fair Value			50,762,000	[8],[9]
Securities, interest rate			3.251%	[8],[9]
Debt instrument, maturity date			Nov. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.309%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			47,107,000	[8],[9]
Fair Value			48,594,000	[8],[9]
Securities, interest rate			3.309%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.336%, Due 9/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			48,525,000	[8],[9]
Fair Value			49,858,000	[8],[9]
Securities, interest rate			3.336%	[8],[9]
Debt instrument, maturity date			Sep. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.340%, Due 9/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			55,821,000	[8],[9]
Fair Value			57,416,000	[8],[9]
Securities, interest rate			3.34%	[8],[9]
Debt instrument, maturity date			Sep. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.462%, Due 11/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			24,735,000	[8],[9]
Fair Value			25,193,000	[8],[9]
Securities, interest rate			3.462%	[8],[9]
Debt instrument, maturity date			Nov. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	88,292,000	[8]	100,441,000	[8]
Fair Value	92,413,000	[8]	101,367,000	[8]
Securities, interest rate	3.50%	[8]	3.50%	[8]
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 1/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	160,654,000	[8]	179,924,000	[8]
Fair Value	168,152,000	[8]	181,582,000	[8]
Securities, interest rate	3.50%	[8]	3.50%	[8]
Debt instrument, maturity date	Jan. 01, 2026	[8]	Jan. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	90,895,000	[8]	4,139,000
Fair Value	95,137,000	[8]	4,177,000
Securities, interest rate	3.50%	[8]	3.50%
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	59,227,000	[8]	16,274,000
Fair Value	61,991,000	[8]	16,424,000
Securities, interest rate	3.50%	[8]	3.50%
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount			99,910,000	[8]
Fair Value			100,831,000	[8]
Securities, interest rate			3.50%	[8]
Debt instrument, maturity date			Dec. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 1/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	93,007,000	[8]	150,000,000
Fair Value	97,348,000	[8]	151,031,000
Securities, interest rate	3.50%	[8]	3.50%
Debt instrument, maturity date	Jan. 01, 2026	[8]	Jan. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 2/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount			550,000,000
Fair Value			552,234,000
Securities, interest rate			3.50%
Debt instrument, maturity date			Feb. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	93,283,000	[8]	150,000,000
Fair Value	97,637,000	[8]	150,094,000
Securities, interest rate	3.50%	[8]	3.50%
Debt instrument, maturity date	Mar. 01, 2026	[8]	Mar. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount			400,000,000
Fair Value			399,031,000
Securities, interest rate			3.50%
Debt instrument, maturity date			Apr. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.506%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			48,469,000	[8],[9]
Fair Value			50,032,000	[8],[9]
Securities, interest rate			3.506%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.558%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			22,367,000	[8],[9]
Fair Value			22,890,000	[8],[9]
Securities, interest rate			3.558%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.571%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			19,640,000	[8],[9]
Fair Value			20,085,000	[8],[9]
Securities, interest rate			3.571%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.579%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			49,287,000	[8],[9]
Fair Value			50,415,000	[8],[9]
Securities, interest rate			3.579%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.605%, Due 10/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			59,742,000	[8],[9]
Fair Value			61,158,000	[8],[9]
Securities, interest rate			3.605%	[8],[9]
Debt instrument, maturity date			Oct. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.605%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			21,609,000	[8],[9]
Fair Value			22,104,000	[8],[9]
Securities, interest rate			3.605%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.615%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			48,456,000	[8],[9]
Fair Value			49,631,000	[8],[9]
Securities, interest rate			3.615%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.648%, Due 6/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			19,497,000	[8],[9]
Fair Value			20,224,000	[8],[9]
Securities, interest rate			3.648%	[8],[9]
Debt instrument, maturity date			Jun. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.664%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			45,354,000	[8],[9]
Fair Value			46,987,000	[8],[9]
Securities, interest rate			3.664%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.676%, Due 7/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount			6,108,000	[8],[9]
Fair Value			6,364,000	[8],[9]
Securities, interest rate			3.676%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2039	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.679%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			46,360,000	[8],[9]
Fair Value			47,667,000	[8],[9]
Securities, interest rate			3.679%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.683%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			47,674,000	[8],[9]
Fair Value			48,944,000	[8],[9]
Securities, interest rate			3.683%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.688%, Due 5/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			13,923,000	[8],[9]
Fair Value			14,464,000	[8],[9]
Securities, interest rate			3.688%	[8],[9]
Debt instrument, maturity date			May 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.694%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			23,798,000	[8],[9]
Fair Value			24,437,000	[8],[9]
Securities, interest rate			3.694%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.755%, Due 5/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			46,830,000	[8],[9]
Fair Value			48,486,000	[8],[9]
Securities, interest rate			3.755%	[8],[9]
Debt instrument, maturity date			May 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.771%, Due 8/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			14,108,000	[8],[9]
Fair Value			14,524,000	[8],[9]
Securities, interest rate			3.771%	[8],[9]
Debt instrument, maturity date			Aug. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.776%, Due 9/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount			29,583,000	[8],[9]
Fair Value			30,984,000	[8],[9]
Securities, interest rate			3.776%	[8],[9]
Debt instrument, maturity date			Sep. 01, 2039	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.830%, Due 7/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			46,251,000	[8],[9]
Fair Value			47,773,000	[8],[9]
Securities, interest rate			3.83%	[8],[9]
Debt instrument, maturity date			Jul. 01, 2040	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.974%, Due 10/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount			38,779,000	[8],[9]
Fair Value			40,546,000	[8],[9]
Securities, interest rate			3.974%	[8],[9]
Debt instrument, maturity date			Oct. 01, 2039	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.983%, Due 9/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount			18,868,000	[8],[9]
Fair Value			19,789,000	[8],[9]
Securities, interest rate			3.983%	[8],[9]
Debt instrument, maturity date			Sep. 01, 2039	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	22,018,000	[8]	25,104,000	[8]
Fair Value	23,228,000	[8]	25,951,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 12/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	69,200,000	[8]	75,493,000	[8]
Fair Value	73,126,000	[8]	76,497,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Dec. 01, 2030	[8]	Dec. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 1/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	44,367,000	[8]	50,369,000	[8]
Fair Value	46,806,000	[8]	52,069,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Jan. 01, 2026	[8]	Jan. 01, 2026	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	63,871,000	[8]	75,088,000	[8]
Fair Value	67,382,000	[8]	77,623,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	26,447,000	[8]	30,566,000
Fair Value	27,901,000	[8]	31,598,000
Securities, interest rate	4.00%	[8]	4.00%
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 1/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	45,217,000	[8]	50,444,000
Fair Value	47,703,000	[8]	51,510,000
Securities, interest rate	4.00%	[8]	4.00%
Debt instrument, maturity date	Jan. 01, 2026	[8]	Jan. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 12/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	20,463,000	[8]	31,096,000
Fair Value	21,447,000	[8]	31,859,000
Securities, interest rate	4.00%	[8]	4.00%
Debt instrument, maturity date	Dec. 01, 2025	[8]	Dec. 01, 2025
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 12/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			22,837,000	[8]
Fair Value			23,554,000	[8]
Securities, interest rate			4.00%	[8]
Debt instrument, maturity date			Dec. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	8,856,000	[8]	11,035,000	[8]
Fair Value	9,343,000	[8]	11,382,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2024	[8]	Oct. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 1/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	32,633,000	[8]	41,384,000	[8]
Fair Value	34,427,000	[8]	42,683,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Jan. 01, 2025	[8]	Jan. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 1/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount			65,069,000	[8]
Fair Value			67,265,000	[8]
Securities, interest rate			4.00%	[8]
Debt instrument, maturity date			Jan. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 2/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	34,866,000	[8]	43,086,000	[8]
Fair Value	36,783,000	[8]	44,540,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Feb. 01, 2025	[8]	Feb. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 3/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount			43,404,000	[8]
Fair Value			44,869,000	[8]
Securities, interest rate			4.00%	[8]
Debt instrument, maturity date			Mar. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 9/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	77,128,000	[8]	96,940,000	[8]
Fair Value	81,504,000	[8]	98,229,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Sep. 01, 2030	[8]	Sep. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 9/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	18,764,000	[8]	23,974,000	[8]
Fair Value	19,829,000	[8]	24,293,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Sep. 01, 2030	[8]	Sep. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	22,721,000	[8]	27,531,000	[8]
Fair Value	23,970,000	[8]	28,460,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2025	[8]	Oct. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	40,935,000	[8]	49,695,000	[8]
Fair Value	43,257,000	[8]	50,356,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2030	[8]	Oct. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	66,893,000	[8]	74,994,000	[8]
Fair Value	70,688,000	[8]	75,992,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2030	[8]	Oct. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	62,935,000	[8]	74,413,000	[8]
Fair Value	66,507,000	[8]	75,402,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2030	[8]	Oct. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	26,600,000	[8]	29,823,000	[8]
Fair Value	28,062,000	[8]	30,830,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2025	[8]	Oct. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	57,085,000	[8]	74,750,000	[8]
Fair Value	60,324,000	[8]	75,744,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2030	[8]	Oct. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	43,228,000	[8]	49,680,000	[8]
Fair Value	45,604,000	[8]	51,356,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2025	[8]	Oct. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 11/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	43,125,000	[8]	49,461,000	[8]
Fair Value	45,496,000	[8]	51,130,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Nov. 01, 2025	[8]	Nov. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 11/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	44,676,000	[8]	50,118,000	[8]
Fair Value	47,132,000	[8]	51,810,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Nov. 01, 2025	[8]	Nov. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 11/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount			9,941,000	[8]
Fair Value			10,277,000	[8]
Securities, interest rate			4.00%	[8]
Debt instrument, maturity date			Nov. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 2/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	14,685,000	[8]	100,000,000
Fair Value	15,511,000	[8]	102,734,000
Securities, interest rate	4.00%	[8]	4.00%
Debt instrument, maturity date	Feb. 01, 2026	[8]	Feb. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.063%, Due 6/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount			19,102,000	[8],[9]
Fair Value			20,082,000	[8],[9]
Securities, interest rate			4.063%	[8],[9]
Debt instrument, maturity date			Jun. 01, 2039	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.096%, Due 9/1/2039 [Member]
Investment Holdings [Line Items]
Face Amount			24,491,000	[8],[9]
Fair Value			25,701,000	[8],[9]
Securities, interest rate			4.096%	[8],[9]
Debt instrument, maturity date			Sep. 01, 2039	[8],[9]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 5/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			12,186,000	[8]
Fair Value			12,856,000	[8]
Securities, interest rate			4.50%	[8]
Debt instrument, maturity date			May 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 6/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	13,989,000	[8]	20,005,000	[8]
Fair Value	14,918,000	[8]	20,980,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Jun. 01, 2024	[8]	Jun. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 5/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			13,063,000	[8]
Fair Value			13,700,000	[8]
Securities, interest rate			4.50%	[8]
Debt instrument, maturity date			May 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 6/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			17,943,000	[8]
Fair Value			18,817,000	[8]
Securities, interest rate			4.50%	[8]
Debt instrument, maturity date			Jun. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 9/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	17,028,000	[8]	21,594,000	[8]
Fair Value	18,158,000	[8]	22,647,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Sep. 01, 2024	[8]	Sep. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 9/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			21,095,000	[8]
Fair Value			22,123,000	[8]
Securities, interest rate			4.50%	[8]
Debt instrument, maturity date			Sep. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 10/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	25,850,000	[8]	36,292,000	[8]
Fair Value	27,566,000	[8]	38,062,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Oct. 01, 2024	[8]	Oct. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 9/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			1,937,000	[8]
Fair Value			2,031,000	[8]
Securities, interest rate			4.50%	[8]
Debt instrument, maturity date			Sep. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 11/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	36,472,000	[8]	11,631,000	[8]
Fair Value	38,893,000	[8]	12,198,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Nov. 01, 2024	[8]	Nov. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 10/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	28,118,000	[8]	38,299,000	[8]
Fair Value	29,985,000	[8]	40,166,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Oct. 01, 2024	[8]	Oct. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 11/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount			49,978,000	[8]
Fair Value			52,415,000	[8]
Securities, interest rate			4.50%	[8]
Debt instrument, maturity date			Nov. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 10/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	23,425,000	[8]	29,910,000	[8]
Fair Value	24,980,000	[8]	31,368,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Oct. 01, 2024	[8]	Oct. 01, 2024	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 4/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	25,704,000	[8]	28,916,000	[8]
Fair Value	27,491,000	[8]	29,998,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Apr. 01, 2030	[8]	Apr. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 5/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	39,840,000	[8]	48,182,000	[8]
Fair Value	42,609,000	[8]	49,984,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	May 01, 2030	[8]	May 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 6/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	23,887,000	[8]	33,361,000	[8]
Fair Value	25,473,000	[8]	35,050,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Jun. 01, 2025	[8]	Jun. 01, 2025	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 10/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	46,023,000	[8]	49,664,000	[8]
Fair Value	49,222,000	[8]	51,522,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Oct. 01, 2030	[8]	Oct. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 11/1/2030 [Member]
Investment Holdings [Line Items]
Face Amount	47,260,000	[8]	50,338,000	[8]
Fair Value	50,545,000	[8]	52,221,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Nov. 01, 2030	[8]	Nov. 01, 2030	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 2/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	44,953,000	[8]	300,000,000
Fair Value	47,937,000	[8]	314,109,000
Securities, interest rate	4.50%	[8]	4.50%
Debt instrument, maturity date	Feb. 01, 2026	[8]	Feb. 01, 2026
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 5.500%, Due 9/1/2023 [Member]
Investment Holdings [Line Items]
Face Amount			32,265,000	[8]
Fair Value			34,714,000	[8]
Securities, interest rate			5.50%	[8]
Debt instrument, maturity date			Sep. 01, 2023	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 5.500%, Due 2/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount			200,000,000
Fair Value			213,594,000
Securities, interest rate			5.50%
Debt instrument, maturity date			Feb. 01, 2041
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 6.000%, Due 5/1/2037 [Member]
Investment Holdings [Line Items]
Face Amount			8,749,000	[8]
Fair Value			9,401,000	[8]
Securities, interest rate			6.00%	[8]
Debt instrument, maturity date			May 01, 2037	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 6.000%, Due 4/1/2038 [Member]
Investment Holdings [Line Items]
Face Amount			14,299,000	[8]
Fair Value			15,555,000	[8]
Securities, interest rate			6.00%	[8]
Debt instrument, maturity date			Apr. 01, 2038	[8]
Fannie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	51,065,000	[8]
Fair Value	53,448,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Mar. 01, 2026	[8]
Freddie Mac Pools [Member]
Investment Holdings [Line Items]
Percent of Investments in Securities	71.20%	[1]	88.60%	[1]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member]
Investment Holdings [Line Items]
Face Amount	732,465,000		597,980,000
Fair Value	767,119,000		612,039,000
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 2.983%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	48,696,000	[7],[8]
Fair Value	50,838,000	[7],[8]
Securities, interest rate	2.983%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.025%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	49,029,000	[7],[8]
Fair Value	51,159,000	[7],[8]
Securities, interest rate	3.025%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.272%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	45,131,000	[7],[8]
Fair Value	46,984,000	[7],[8]
Securities, interest rate	3.272%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.236%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount	42,661,000	[7],[8]
Fair Value	44,466,000	[7],[8]
Securities, interest rate	3.236%	[7],[8]
Debt instrument, maturity date	Dec. 01, 2040	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.645%, Due 6/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	46,075,000	[7],[8]
Fair Value	48,390,000	[7],[8]
Securities, interest rate	3.645%	[7],[8]
Debt instrument, maturity date	Jun. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.423%, Due 9/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	48,337,000	[7],[8]
Fair Value	50,535,000	[7],[8]
Securities, interest rate	3.423%	[7],[8]
Debt instrument, maturity date	Sep. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.240%, Due 2/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	39,068,000	[7],[8]
Fair Value	40,779,000	[7],[8]
Securities, interest rate	3.24%	[7],[8]
Debt instrument, maturity date	Feb. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.246%, Due 1/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount	46,017,000	[7],[8]
Fair Value	48,037,000	[7],[8]
Securities, interest rate	3.246%	[7],[8]
Debt instrument, maturity date	Jan. 01, 2041	[7],[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 4/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount	180,607,000	[8]
Fair Value	188,414,000	[8]
Securities, interest rate	3.50%	[8]
Debt instrument, maturity date	Apr. 01, 2026	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 10/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	57,327,000	[8]	73,474,000	[8]
Fair Value	60,183,000	[8]	75,689,000	[8]
Securities, interest rate	4.00%	[8]	4.00%	[8]
Debt instrument, maturity date	Oct. 01, 2025	[8]	Oct. 01, 2025	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 5.500%, Due 9/1/2023 [Member]
Investment Holdings [Line Items]
Face Amount			4,998,000	[8]
Fair Value			5,360,000	[8]
Securities, interest rate			5.50%	[8]
Debt instrument, maturity date			Sep. 01, 2023	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.052%, Due 1/1/2041 [Member]
Investment Holdings [Line Items]
Face Amount			45,411,000	[8],[9]
Fair Value			46,424,000	[8],[9]
Securities, interest rate			3.052%	[8],[9]
Debt instrument, maturity date			Jan. 01, 2041	[8],[9]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.200%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			50,012,000	[8],[9]
Fair Value			51,281,000	[8],[9]
Securities, interest rate			3.20%	[8],[9]
Debt instrument, maturity date			Dec. 01, 2040	[8],[9]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.247%, Due 12/1/2040 [Member]
Investment Holdings [Line Items]
Face Amount			49,646,000	[9]
Fair Value			50,980,000	[9]
Securities, interest rate			3.247%	[9]
Debt instrument, maturity date			Dec. 01, 2040	[9]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 3/1/2026 [Member]
Investment Holdings [Line Items]
Face Amount			200,000,000
Fair Value			199,938,000
Securities, interest rate			3.50%
Debt instrument, maturity date			Mar. 01, 2026
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 7/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	30,445,000	[8]	48,351,000	[8]
Fair Value	32,280,000	[8]	50,527,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Jul. 01, 2024	[8]	Jul. 01, 2024	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 2/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	34,570,000	[8]	43,717,000	[8]
Fair Value	36,660,000	[8]	45,739,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Feb. 01, 2025	[8]	Feb. 01, 2025	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 12/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	11,485,000	[8]	15,509,000	[8]
Fair Value	12,177,000	[8]	16,207,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Dec. 01, 2024	[8]	Dec. 01, 2024	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 12/1/2024 [Member]
Investment Holdings [Line Items]
Face Amount	10,567,000	[8]	15,096,000	[8]
Fair Value	11,204,000	[8]	15,775,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Dec. 01, 2024	[8]	Dec. 01, 2024	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 1/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	25,440,000	[8]	33,201,000	[8]
Fair Value	26,974,000	[8]	34,696,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	Jan. 01, 2025	[8]	Jan. 01, 2025	[8]
Freddie Mac Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.500%, Due 5/1/2025 [Member]
Investment Holdings [Line Items]
Face Amount	17,010,000	[8]	18,565,000	[8]
Fair Value	18,039,000	[8]	19,423,000	[8]
Securities, interest rate	4.50%	[8]	4.50%	[8]
Debt instrument, maturity date	May 01, 2025	[8]	May 01, 2025	[8]
Ginnie Mae Pools [Member]
Investment Holdings [Line Items]
Percent of Investments in Securities	13.70%	[1]	23.40%	[1]
Ginnie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member]
Investment Holdings [Line Items]
Face Amount	139,825,000		154,939,000
Fair Value	147,820,000		161,401,000
Ginnie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 7/20/2040 [Member]
Investment Holdings [Line Items]
Face Amount	78,468,000	[7],[8]	84,444,000	[8],[9]
Fair Value	82,891,000	[7],[8]	87,841,000	[8],[9]
Securities, interest rate	3.50%	[7],[8]	3.50%	[8],[9]
Debt instrument, maturity date	Jul. 20, 2040	[7],[8]	Jul. 20, 2040	[8],[9]
Ginnie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 3.500%, Due 7/20/2040 [Member]
Investment Holdings [Line Items]
Face Amount	44,331,000	[7],[8]	49,868,000	[8],[9]
Fair Value	46,830,000	[7],[8]	51,874,000	[8],[9]
Securities, interest rate	3.50%	[7],[8]	3.50%	[8],[9]
Debt instrument, maturity date	Jul. 20, 2040	[7],[8]	Jul. 20, 2040	[8],[9]
Ginnie Mae Pools [Member] | Mortgage Pass-Through Agency RMBS [Member] | 4.000%, Due 1/20/2040 [Member]
Investment Holdings [Line Items]
Face Amount	17,026,000	[7],[8]	20,627,000	[8],[9]
Fair Value	$ 18,099,000	[7],[8]	$ 21,686,000	[8],[9]
Securities, interest rate	4.00%	[7],[8]	4.00%	[8],[9]
Debt instrument, maturity date	Jan. 20, 2040	[7],[8]	Jan. 20, 2040	[8],[9]

[1] Percentage of net assets.

[2] Zero coupon bond, rate shown represents purchase yield.

[3] Securities exempt from registration under Rule 144A of the Securities Act of 1933. These securities may only be resold in transactions exempt from registration, normally to qualified institutional buyers. At December 31, 2011, the fair value of these securities amounted to $18,675 or 1.7% of net assets.

[4] Securities exempt from registration under Rule 144A of the Securities Act of 1933. These securities may only be resold in transactions exempt from registration, normally to qualified institutional buyers. At December 31, 2010, the fair value of these securities amounted to $20,478 or 3.0% of net assets.

[5] Non-income producing security.

[6] The interest rate swap effective date is December 19, 2012 and does not accrue any income or expense until that date.

[7] The coupon rate shown on floating or adjustable rate securities represents the rate at December 31, 2011.

[8] Securities or a portion of the securities are pledged as collateral for repurchase agreements or interest rate swap contracts.

[9] The coupon rate shown on floating or adjustable rate securities represents the rate at December 31, 2010.