Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Debt Disclosure [Line Items]
Fair Value Measurements, Recurring Basis, Transfers From Level 2 To Level 1	$ 0		$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	5,143		266
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	$ 3,561	[1]	$ 0	[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.