Fair Value of Financial Instruments - Quantitative Information About Significant Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified															9 Months Ended	12 Months Ended			9 Months Ended				9 Months Ended		12 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2014 Equity warrant assets Other assets		Jun. 30, 2014 Equity warrant assets Other assets		Sep. 30, 2013 Equity warrant assets Other assets		Jun. 30, 2013 Equity warrant assets Other assets		Sep. 30, 2014 Level 3 Other venture capital investments Fair value accounting	Dec. 31, 2013 Level 3 Other venture capital investments Fair value accounting	Dec. 31, 2013 Level 3 Other securities Fair value accounting		Sep. 30, 2014 Level 3 Equity warrant assets Lower Limit	Sep. 30, 2014 Level 3 Equity warrant assets Upper Limit	Sep. 30, 2014 Level 3 Equity warrant assets Investments	Dec. 31, 2013 Level 3 Equity warrant assets Investments	Sep. 30, 2014 Level 3 Equity warrant assets Other assets		Dec. 31, 2013 Level 3 Equity warrant assets Other assets		Sep. 30, 2014 Level 3 Equity Warrant Asset, Private Portfolio Investments	Dec. 31, 2013 Level 3 Equity Warrant Asset, Private Portfolio Investments	Sep. 30, 2014 Level 3 Equity Warrant Asset, Private Portfolio Other assets		Dec. 31, 2013 Level 3 Equity Warrant Asset, Private Portfolio Other assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 1,216,171	$ 1,177,228	$ 1,314,951	$ 1,134,038	$ 938,244	$ 859,141	$ 93,397	[1]	$ 87,151	[1]	$ 88,126	[1]	$ 73,229	[1]	$ 43,863	$ 32,839	$ 319,249				$ 529	$ 24,217					$ 92,868	$ 75,674
Valuation Technique															Private company equity pricing	Private company equity pricing	Modified stock price						Modified Black-Scholes option pricing model		Modified Black-Scholes option pricing model				Modified Black-Scholes option pricing model		Modified Black-Scholes option pricing model
Volatility																							43.90%		41.30%				38.20%		40.10%
Risk-Free interest rate																							2.10%		1.70%				1.00%		0.80%
Sales restrictions discount																	12.00%	[2]	1000.00%	2000.00%			15.70%	[2]	13.70%	[2]
Marketability discount																													20.00%	[3]	22.50%	[3]
Remaining life assumption																													45.00%	[4]	45.00%	[4]

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

[2] We adjust quoted market prices of public companies, which are subject to certain sales restrictions. Sales restriction discounts generally range from 10 percent to 20 percent depending on the duration of the sales restrictions, which typically range from 3 to 6 months.

[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, including 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 estimate of the actual remaining life, which we determine by utilizing historical data on cancellations and exercises. At September 30, 2014, the weighted average contractual remaining term was 6.25 years, compared to our estimated remaining life of 2.81 years. On a quarterly basis, a sensitivity analysis is performed on our remaining life assumption.