Fair value, Financial Instruments Summary (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Financial assets    
Investment securities available for sale $ 36,696 $ 30,163
Carrying Value [Member] | Level 1 [Member]
   
Financial assets    
Cash Fair Value Disclosure 23,271,435 55,557,541
Investment securities available for sale 4,816,213 10,207,805
Carrying Value [Member] | Level 2 [Member]
   
Financial assets    
Cash Equivalents Fair Value Disclosure 3,834,563 7,228,475
Investment securities available for sale 31,880,069 19,955,487
Federal Home Loan Bank stock 2,396,600 2,647,000
Loans held for sale 19,729,508 16,168,405
Loans 306,467,001 353,186,646
Impaired loans 57,753,817 51,867,625
Other real estate owned 11,212,437 874,246
Accrued interest receivable 1,910,147 2,046,524
Financial liabilities    
Deposits 450,419,908 485,521,052
FHLB borrowings 29,000,000 37,750,000
Trust preferred securities 8,764,000 8,764,000
Other borrowings 5,062,344 5,778,661
Accrued interest payable 703,817 592,283
Carrying Value [Member] | Level 3 [Member]
   
Financial assets    
Impaired loans 14,700,558 12,787,473
Other real estate owned 6,464,625 8,302,921
Bank owned life insurance 6,159,335 6,065,305
Estimated Fair Value [Member] | Level 1 [Member]
   
Financial assets    
Cash Fair Value Disclosure 23,271,435 55,557,541
Investment securities available for sale 4,816,213 10,207,805
Estimated Fair Value [Member] | Level 2 [Member]
   
Financial assets    
Cash Equivalents Fair Value Disclosure 3,834,563 7,228,475
Investment securities available for sale 31,880,069 19,955,487
Federal Home Loan Bank stock 2,396,600 2,647,000
Loans held for sale 19,729,508 16,168,405
Loans 305,208,432 353,349,981
Impaired loans 57,753,817 51,867,625
Other real estate owned 11,212,437 874,246
Accrued interest receivable 1,910,147 2,046,524
Financial liabilities    
Deposits 454,971,918 487,915,609
FHLB borrowings 29,167,554 37,963,672
Trust preferred securities 8,764,000 8,764,000
Other borrowings 5,062,344 5,778,661
Accrued interest payable 703,817 592,283
Estimated Fair Value [Member] | Level 3 [Member]
   
Financial assets    
Impaired loans 14,700,558 12,787,473
Other real estate owned 6,464,625 8,302,921
Bank owned life insurance $ 6,159,335 $ 6,065,305