Securities (Detail) - Changes In Credit Losses Recognized In Earnings - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative amount recognized at the beginning of the year		$ 23,880	$ 32,422	$ 38,803
OTTI included in earnings:
Losses on securities that previously had OTTI	[1]	0	28	0
Losses on securities that did not previously have OTTI	[1]	0	0	408
Reduction for securities sales	[2]	(171)	(8,570)	(6,789)
Cumulative amount recognized at the end of the year		$ 23,709	$ 23,880	$ 32,422

[1] Included in net securities gains in the Consolidated Statements of Income.

[2] These reductions were driven by the sale of one CMO with a carrying value of $1.3 million during the year ended December 31, 2015, one CDO with a carrying value of $1.3 million during the year ended December 31, 2014, and one CDO with a carrying value of zero during the year ended December 31, 2013.