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Fair Value Disclosures - Fair Value Measurements, Recurring and Nonrecurring (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets $ 18,934 $ 29,523
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 807,180 1,165,889
Trading securities 0 0
Marketable Securities 807,180 1,165,889
Derivative Assets 0 0
Assets at fair value 807,180 1,165,889
Financial derivatives, Liabilities 0 12
Liabilities at fair value 0 12
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,629,653 1,269,334
Trading securities 0 0
Marketable Securities 1,629,653 1,269,334
Derivative Assets 19,676 31,173
Assets at fair value 1,649,329 1,300,507
Financial derivatives, Liabilities 91,116 149,979
Liabilities at fair value 91,116 149,979
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,302 63,159
Trading securities 977 1,247
Marketable Securities 66,279 64,406
Derivative Assets 0 0
Assets at fair value 6,834,045 6,421,447
Financial derivatives, Liabilities 329 691
Liabilities at fair value 329 691
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 2,502,135 2,498,382
Trading securities 977 1,247
Marketable Securities 2,503,112 2,499,629
Derivative Assets 19,676 31,173
Assets at fair value 9,290,554 8,887,843
Financial derivatives, Liabilities 91,445 150,682
Liabilities at fair value 91,445 150,682
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 0 0
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 0 0
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 7,664 666,988
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 7,664 666,988
Farmer Mac Guarantee [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 5,138,756 4,766,258
Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 5,138,756 4,766,258
Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 5,138,756 4,766,258
Farm & Ranch Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Farm & Ranch Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Farm & Ranch Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 3,598,523 3,426,489
Farm & Ranch Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 3,598,523 3,426,489
USDA Guarantees - Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
USDA Guarantees - Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
USDA Guarantees - Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 25,708 26,681
USDA Guarantees - Farmer Mac Guaranteed Securities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 25,708 26,681
Farmer Mac Guaranteed Securities - Rural Utilities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
   
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 [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
   
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 [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,514,525 1,313,088
Farmer Mac Guaranteed Securities - Rural Utilities [Member] | Farmer Mac Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,514,525 1,313,088
Financing Loans [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value   0
Financing Loans [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value   0
Financing Loans [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value   657,154
Financing Loans [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value   657,154
loans held for investment [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 0 0
loans held for investment [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 0 0
loans held for investment [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 5,584 8,130
loans held for investment [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 5,584 8,130
REO [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 0 0
REO [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 0 0
REO [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 2,080 1,704
REO [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets at fair value 2,080 1,704
USDA Guaranteed Securities [Member] | USDA Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Trading securities 0 0
Marketable Securities 0 0
USDA Guaranteed Securities [Member] | USDA Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Trading securities 0 0
Marketable Securities 0 0
USDA Guaranteed Securities [Member] | USDA Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,566,691 1,486,595
Trading securities 62,319 104,188
Marketable Securities 1,629,010 1,590,783
USDA Guaranteed Securities [Member] | USDA Guarantee [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 1,566,691 1,486,595
Trading securities 62,319 104,188
Marketable Securities 1,629,010 1,590,783
Auction-rate certificates backed by Government guaranteed student loans [Member] | Floating Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,088 63,159
Auction-rate certificates backed by Government guaranteed student loans [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
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 [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
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 [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,088 63,159
Auction-rate certificates backed by Government guaranteed student loans [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,088 63,159
Asset-backed Securities [Member] | Floating Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 163,696 151,044
Trading securities 977 1,247
Asset-backed Securities [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities   6,501
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 163,696 151,044
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 163,696 151,044
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities   0
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities   6,501
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities   0
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities   6,501
Asset-backed Securities [Member] | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 0 0
Asset-backed Securities [Member] | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 0 0
Asset-backed Securities [Member] | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 977 1,247
Asset-backed Securities [Member] | Trading Account Assets [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 977 1,247
Corporate Debt Securities [Member] | Floating Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 114,773 76,763
Corporate Debt Securities [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,188 52,416
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 114,773 76,763
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 114,773 76,763
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,188 52,416
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 65,188 52,416
Collateralized Mortgage Backed Securities [Member] | Floating Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 751,707 712,859
Collateralized Mortgage Backed Securities [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 9,141 [1] 2,065
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 751,493 712,859
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 214 0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 751,707 712,859
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 9,141 2,065
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 9,141 2,065
Subordinated Debt [Member] | Floating Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 63,385 57,431
Subordinated Debt [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Subordinated Debt [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 63,385 57,431
Subordinated Debt [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Subordinated Debt [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 63,385 57,431
Preferred Stock [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 83,455 87,086
Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 83,455 87,086
Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 83,455 87,086
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
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 [Member] | Level 2 [Member]
   
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 [Member] | Level 3 [Member]
   
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 [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities   0
Taxable Municipal Bonds [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 26,744  
Taxable Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0  
Taxable Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 26,744  
Taxable Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0  
Taxable Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 26,744  
Senior Agency Debt Securities [Member] | Floating Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 25,011 50,055
Senior Agency Debt Securities [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 326,767 73,114
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 25,011 50,055
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Floating Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 25,011 50,055
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 326,767 73,114
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 0 0
Senior Agency Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 326,767 73,114
US Treasury Securities [Member] | Fixed Interest Rate [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 807,180 1,165,889
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 807,180 1,165,889
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Interest Rate [Member] | Level 2 [Member]
   
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 [Member] | Level 3 [Member]
   
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 [Member] | Fair Value [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities $ 807,180 $ 1,165,889
[1] Fair value includes $7.7 million of an interest-only security with a notional amount of $152.4 million.