Borrowed Funds - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Short-term debt		$ 12,000,000
Securities sold under agreements to repurchase	1,787,270,000	1,900,000,000
Accrued interest payable	16,000	18,000
Wells Fargo Bank 1.25% due 2012
Debt Instrument [Line Items]
Revolving line of credit, maximum borrowing capacity	25,000,000
Interest rate based on LIBOR	1.00 percent above LIBOR
Debt instrument, interest rate based on prime lending rate	1.75 percent below Prime
Revolving line of credit, commitment fee for unused portion	0.20%
Short-term debt		$ 10,000,000

Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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The carrying value as of the balance sheet date of securities that an institution sells and agrees to repurchase (the identical or substantially the same securities) as a seller-borrower at a specified date for a specified price, also known as a repurchase agreement, or repo. Most repos involve obligations of the federal government or its agencies, but other financial instruments, such as commercial paper, banker's acceptances, and negotiable certificates of deposit, are sometimes used in repos.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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