Loans, Leases and Allowance for Credit Losses - Changes in Accretable Discount for Loans Purchased with Credit Quality Deterioration (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 19,156		$ 28,164
Reclassification from non-accretable to accretable yield (1)	430	[1]	1,466	[1]
Accretion to interest income	(1,078)		(2,404)
Reversal of fair value adjustments upon disposition of loans	(552)		(395)
Balance at end of period	$ 17,956		$ 26,831

[1] The primary drivers of reclassification from non-accretable to accretable yield resulted from changes in estimated cash flows.