Investment Securities Available for Sale - Amortized Cost, Estimated Market Value and Credit Rating of Corporate Debt Securities (Detail) (USD $) In Thousands, unless otherwise specified			6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 BankAmerica Capital [Member]	Jun. 30, 2013 Chase Capital [Member]	Jun. 30, 2013 Wells Fargo Capital [Member]	Jun. 30, 2013 Huntington Capital [Member]	Jun. 30, 2013 Keycorp Capital [Member]	Jun. 30, 2013 PNC Capital [Member]	Jun. 30, 2013 State Street Capital [Member]	Jun. 30, 2013 SunTrust Capital [Member]	Jun. 30, 2013 Corporate Debt Securities [Member]	Dec. 31, 2012 Corporate Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 236,437	$ 223,953	$ 15,000	$ 10,000	$ 5,000	$ 5,000	$ 5,000	$ 5,000	$ 5,000	$ 5,000	$ 55,000	$ 55,000
Estimated Market Value	$ 226,753	$ 213,593	$ 11,875	$ 8,112	$ 4,125	$ 3,950	$ 4,050	$ 4,100	$ 4,200	$ 4,150	$ 44,562	$ 43,470
Credit Rating Moody's/S&P			Ba2/BB+	Baa2/BBB	A3/A-	Baa3/BB+	Baa3/BBB-	Baa2/BBB	A3/BBB+	Baa3/BB+