Securities - Net Gains and Losses on Trading Account Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 253	$ 282	$ 493	$ 576
Net mark-to-market gains (losses)	0	(377)	(3)	(380)
Net gain (loss) on trading account securities	$ 253	$ (95)	$ 490	$ 196