Quantitative Information About Significant Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 828,326		$ 814,526		$ 799,962		$ 679,960		$ 620,157		$ 547,608
Other venture capital investments | Fair value accounting
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	120,111	[1]
Valuation Technique	Private company equity pricing	[1]
Equity Warrant Asset | Other assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 68,619	[2]	$ 65,217	[2]	$ 63,030	[2]	$ 49,777	[2]	$ 46,260	[2]	$ 43,537	[2]
Valuation Technique	Modifed Black-Scholes option pricing model
Volatility	51.20%	[1]
Risk-Free interest rate	0.40%	[1]
Marketability discount	15.00%	[1],[3]
Remaining life assumption	40.00%	[1],[4]

[1] In determining the fair value of our other venture capital investment portfolio, we evaluate a variety of factors related to each underlying private portfolio company including, but not limited to, actual and forecasted results, cash position, recent or planned transactions and market comparable companies. Additionally, we have ongoing communication with the portfolio companies and venture capital fund managers, to determine whether there is a material change in fair value. These factors are specific to each portfolio company and a weighted average or range of values of the unobservable inputs is not meaningful.

[2] Realized and unrealized gains (losses) are recorded on the line item "gains on derivative instruments, net", a component of noninterest income.

[3] Our marketability discount is applied to all private company warrants to account for a general lack of liquidity due to the private nature of the associated underlying company. The quantitative measure used is based on long-run averages and is influenced over time by various factors, such as market conditions. On a quarterly basis, a sensitivity analysis is performed on our marketability discount.

[4] We adjust the contractual remaining term of private company warrants based on our best estimate of the actual remaining life, which we determine by utilizing historical data on cancellations and exercises. At June 30, 2012, the weighted average contractual remaining term was 6.5 years, compared to our estimated remaining life of 2.6 years. On a quarterly basis, a sensitivity analysis is performed on our remaining life assumption.