Loans, Leases and Allowance for Credit Losses - Changes in Accretable Discount for Loans Purchased with Credit Quality Deterioration (Detail) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Additions			$ 857	$ 0	$ 0
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets		$ 7,000
Balance at beginning of period			19,156	28,164	7,072
Reclassifications from non-accretable to accretable yield (1)	[1]		1,747	6,052	9,817
Accretion to interest income			(3,996)	(7,185)	(7,182)
Reversal of fair value adjustments upon disposition of loans			(1,877)	(7,875)	(3,861)
Balance at end of period			15,925	19,156	28,164
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets			$ 38	$ 0	$ 22,318

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