Securities - Amortized Cost, Estimated Fair Value and Credit Rating of Corporate Debt Securities (Detail) (USD $) In Thousands, unless otherwise specified			6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 BankAmerica Capital [Member]	Jun. 30, 2014 Chase Capital [Member]	Jun. 30, 2014 Wells Fargo Capital [Member]	Jun. 30, 2014 Huntington Capital [Member]	Jun. 30, 2014 Keycorp Capital [Member]	Jun. 30, 2014 PNC Capital [Member]	Jun. 30, 2014 State Street Capital [Member]	Jun. 30, 2014 SunTrust Capital [Member]	Jun. 30, 2014 Corporate Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost			$ 15,000	$ 10,000	$ 5,000	$ 5,000	$ 5,000	$ 5,000	$ 5,000	$ 5,000	$ 55,000
Estimated Fair Value	$ 485,124	$ 495,082	$ 12,750	$ 8,740	$ 4,300	$ 4,175	$ 4,250	$ 4,300	$ 4,300	$ 4,275	$ 47,090
Credit Rating Moody's/S&P			Ba1/BB+	Baa2/BBB	A3/A-	Baa3/BB+	Baa3/BBB-	Baa2/BBB	A3/BBB+	Baa3/BB+