Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Debt Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ 312		$ 1,146		$ 5,953		$ 2,256
Fair value accounting | Non-marketable securities
Debt Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ 0	[1]	$ 978	[1]	$ 3,561	[1]	$ 1,573	[1]

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