Securities (Net Gains and Losses on Trading Account Securities) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 1,109	$ 829	$ 878
Net mark-to-market gains (losses)	(53)	0	(429)
Net gain on trading account securities	$ 1,056	$ 829	$ 449