Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Debt Disclosure [Line Items]
Investments transferred out of Level 3	$ 6,245		$ 312		$ 381,696		$ 5,953
Fair value accounting | Non-marketable securities
Debt Disclosure [Line Items]
Investments transferred out of Level 3	5,808	[1]	0	[1]	380,262	[1]
Other securities | Fair value accounting | Non-marketable securities
Debt Disclosure [Line Items]
Investments transferred out of Level 3					$ 380,136

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