Short-Term Borrowings and Long-Term Debt (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 30, 2011	Mar. 19, 2004
Line of Credit Facility, Remaining Borrowing Capacity	$ 35,000,000	$ 70,000,000		$ 40,000,000
Securities Loaned					46,400,000
Line of Credit Facility, Interest Rate Description		7.00%
Debt Issuance Cost	1,200,000	974,000	1,200,000
Federal Reserve [Member]
Line of Credit Facility, Remaining Borrowing Capacity	$ 249,700,000	$ 257,700,000	$ 252,900,000