Quantitative Information About Significant Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 859,141		$ 799,962		$ 547,608		$ 409,155
Other venture capital investments | Fair value accounting
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	127,091
Valuation Technique	Private company equity pricing
Equity Warrant Asset | Other assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 66,129	[1]	$ 63,030	[1]	$ 43,537	[1]	$ 40,119
Valuation Technique	Modifed Black-Scholes option pricing model
Volatility	45.20%
Risk-Free interest rate	0.40%
Fair Value Inputs, Discount for Lack of Marketability	22.50%		15.00%
Financial Instruments Fair Value Assumptions Weighted Average Remaining Life	45.00%		40.00%

[1] Realized and unrealized gains are recorded on the line item “gains on derivative instruments, net”, a component of noninterest income.