Borrowed Funds - Schedule of Repayment of Long-Term Borrowings for Securities Sold Under Agreements to Repurchase (Detail) (Long-Term Borrowings [Member], USD $)	Dec. 31, 2012	Dec. 31, 2011
Long-Term Borrowings [Member]
Debt Instrument [Line Items]
2015	$ 125,000,000
2016	92,500,000
2017	220,000,000
Thereafter	150,000,000
Total long-term borrowings for securities sold under agreements to repurchase	$ 587,500,000	$ 587,500,000