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		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period		$ 15,863	$ 17,190	$ 15,925	$ 19,156
Additions due to acquisition		0	0	4,301	857
Reclassifications from non-accretable to accretable yield (1)	[1]	119	597	119	1,292
Accretion to interest income		(901)	(1,056)	(2,570)	(3,146)
Reversal of fair value adjustments upon disposition of loans		(578)	(398)	(3,272)	(1,826)
Balance at end of period		$ 14,503	$ 16,371	$ 14,503	$ 16,371

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