Fair Value Disclosures - Fair Value Measurements, Recurring and Nonrecurring (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Measurements, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 1,179,892	$ 799,266
Trading securities	0	0
Total securities	1,179,892	799,266
Financial derivatives, Assets	0	0
Assets at fair value	1,179,892	799,266
Financial derivatives, Liabilities	3	0
Liabilities at fair value	3	0
Fair Value, Measurements, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,395,058	1,323,215
Trading securities	0	0
Total securities	1,395,058	1,323,215
Financial derivatives, Assets	36,190	40,250
Assets at fair value	1,431,248	1,363,465
Financial derivatives, Liabilities	164,066	158,689
Liabilities at fair value	164,066	158,689
Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	60,034	60,213
Trading securities	1,344	1,796
Total securities	61,378	62,009
Financial derivatives, Assets	0	0
Assets at fair value	6,300,513	5,843,186
Financial derivatives, Liabilities	880	1,335
Liabilities at fair value	880	1,335
Fair Value, Measurements, Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,634,984	2,182,694
Trading securities	1,344	1,796
Total securities	2,636,328	2,184,490
Financial derivatives, Assets	36,190	40,250
Assets at fair value	8,911,653	8,005,917
Financial derivatives, Liabilities	164,949	160,024
Liabilities at fair value	164,949	160,024
Fair Value, Measurements, Nonrecurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value, Measurements, Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	8,981	11,414
Fair Value, Measurements, Nonrecurring | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	8,981	11,414
Farmer Mac Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,648,507	4,289,272
Farmer Mac Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,648,507	4,289,272
Farmer Mac I Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac I Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac I Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,431,588	2,807,627
Farmer Mac I Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,431,588	2,807,627
Farmer Mac II Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac II Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac II Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,975	35,599
Farmer Mac II Guaranteed Securities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,975	35,599
Farmer Mac Guaranteed Securities - Rural Utilities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac Guaranteed Securities - Rural Utilities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Farmer Mac Guaranteed Securities - Rural Utilities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,186,944	1,446,046
Farmer Mac Guaranteed Securities - Rural Utilities | Farmer Mac Guarantee | Fair Value, Measurements, Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,186,944	1,446,046
USDA Guaranteed Securities | USDA Guarantee | Fair Value, Measurements, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Total securities	0	0
USDA Guaranteed Securities | USDA Guarantee | Fair Value, Measurements, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Trading securities	0	0
Total securities	0	0
USDA Guaranteed Securities | USDA Guarantee | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,468,041	1,279,546
Trading securities	122,587	212,359
Total securities	1,590,628	1,491,905
USDA Guaranteed Securities | USDA Guarantee | Fair Value, Measurements, Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,468,041	1,279,546
Trading securities	122,587	212,359
Total securities	1,590,628	1,491,905
Loans Held For Investment | Fair Value, Measurements, Nonrecurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Loans Held For Investment | Fair Value, Measurements, Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Financing Loans | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	7,822	10,118
Financing Receivable [Member] | Fair Value, Measurements, Nonrecurring | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	7,822	10,118
REO | Fair Value, Measurements, Nonrecurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
REO | Fair Value, Measurements, Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
REO | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,159	1,296
REO | Fair Value, Measurements, Nonrecurring | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,159	1,296
Auction-rate certificates backed by Government guaranteed student loans | Floating Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	60,034	60,213
Auction-rate certificates backed by Government guaranteed student loans | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Auction-rate certificates backed by Government guaranteed student loans | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Auction-rate certificates backed by Government guaranteed student loans | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	60,034	60,213
Auction-rate certificates backed by Government guaranteed student loans | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	60,034	60,213
Asset-backed Securities | Floating Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	167,045	178,560
Trading securities	1,344	1,796
Asset-backed Securities | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9,735
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	167,045	178,560
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	167,045	178,560
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9,735
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Asset-backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9,735
Asset-backed Securities | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	0
Asset-backed Securities | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	0
Asset-backed Securities | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,344	1,796
Asset-backed Securities | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,344	1,796
Government/GSE Guaranteed Mortgage Backed Securities | Floating Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	743,444	764,038
Government/GSE Guaranteed Mortgage Backed Securities | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,537	3,360
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	743,444	764,038
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	743,444	764,038
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,537	3,360
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Government/GSE Guaranteed Mortgage Backed Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,537	3,360
Corporate Debt Securities | Floating Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	78,819	73,833
Corporate Debt Securities | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	52,681	38,699
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	78,819	73,833
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	78,819	73,833
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	52,681	38,699
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Corporate Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	52,681	38,699
GSE Subordinated Debt | Floating Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	57,170	52,562
GSE Subordinated Debt | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
GSE Subordinated Debt | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	57,170	52,562
GSE Subordinated Debt | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
GSE Subordinated Debt | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	57,170	52,562
Commercial Paper [Member] | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	19,997	10,000
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		10,000
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		10,000
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	19,997
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	19,997
GSE Preferred stock | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	85,859	84,878
GSE Preferred stock | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
GSE Preferred stock | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	85,859	84,878
GSE Preferred stock | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
GSE Preferred stock | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	85,859	84,878
Senior Agency Debt Securities | Floating Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	50,056	38,032
Senior Agency Debt Securities | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	127,715	79,253
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	50,056
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	50,056
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	127,715	117,285
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Senior Agency Debt Securities | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	127,715	117,285
US Treasury Securities [Member] | Fixed Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,179,892	799,266
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,179,892	799,266
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 1,179,892	$ 799,266