Securities (Narrative) (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Disclosure Securities Narrative [Abstract]
Available-for-sale and held-to-maturity securities, pledged, carrying value	$ 541,700	$ 353,100
Securities pledged as collateral which may be sold or re-pledged by the secured party	246,700	86,500
Investments securities from one issuer that exceeds maximum percentage	$ 0	$ 0
Percentage of securities portfolio from one issuer, maximum	10.00%	10.00%
Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	$ 303,200	$ 616,800
Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses	6,300	10,900
Other than Temporary Impairment Losses, Investments	$ 0	$ 0