Fair Value of Financial Instruments - Additional Information about Level 3 Assets Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,316,784		$ 1,314,951
Total Realized and Unrealized Gains Included in Income	73,388		240,245
Purchases	60,040		45,125
Sales	(14,804)		(90,347)
Issuances	2,083		3,417
Distributions and Other Settlements	(40,834)		(41,324)
Transfers Out of Level 3	(243)		(16,710)
Ending Balance	1,396,414		1,455,357
Equity warrant assets | Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	114,698	[1]	99,891	[1]
Total Realized and Unrealized Gains Included in Income	20,084	[1]	24,378	[1]
Purchases	0	[1]	0	[1]
Sales	(14,765)	[1]	(39,993)	[1]
Issuances	2,083	[1]	3,417	[1]
Distributions and Other Settlements	404	[1]	626	[1]
Transfers Out of Level 3	(243)	[1]	(677)	[1]
Ending Balance	122,261	[1]	87,642	[1]
Non-marketable securities | Fair value accounting
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,202,086	[2]	1,215,060	[2]
Total Realized and Unrealized Gains Included in Income	53,304	[2]	215,867	[2]
Purchases	60,040	[2]	45,125	[2]
Sales	(39)	[2]	(50,354)	[2]
Issuances	0	[2]	0	[2]
Distributions and Other Settlements	(41,238)	[2]	(41,950)	[2]
Transfers Out of Level 3	0	[2]	(16,033)	[2]
Ending Balance	1,274,153	[2]	1,367,715	[2]
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,130,882		862,972
Total Realized and Unrealized Gains Included in Income	46,854		111,335
Purchases	58,670		44,455
Sales	0		0
Issuances	0		0
Distributions and Other Settlements	(41,103)		(41,840)
Transfers Out of Level 3	0		0
Ending Balance	1,195,303		976,922
Non-marketable securities | Fair value accounting | Other venture capital investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	71,204		32,839
Total Realized and Unrealized Gains Included in Income	6,450		1,838
Purchases	1,370		670
Sales	(39)		(3,514)
Issuances	0		0
Distributions and Other Settlements	(135)		(3,527)
Transfers Out of Level 3	0		0
Ending Balance	78,850		28,306
Non-marketable securities | Fair value accounting | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance			319,249
Total Realized and Unrealized Gains Included in Income			102,694
Purchases			0
Sales			(46,840)
Issuances			0
Distributions and Other Settlements			3,417
Transfers Out of Level 3			(16,033)
Ending Balance			$ 362,487

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

[2] Realized and unrealized gains (losses) are recorded in the line items “gains on investment securities, net”, and “other noninterest income”, components of noninterest income.