Income Taxes - Schedule of Significant Components of Net Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets
Allowance for loan losses, net of recapture	$ 17,125	$ 16,348
Benefit plan accruals	18,066	16,683
AMT credit	18,378	19,808
Unrealized losses on benefit plans	4,507	5,648
Net operating loss carryforwards	2,041	3,258
Premises and equipment	12,735	20,139
Federal tax credits	422	1,632
Other-than-temporary impairment	3,558	3,573
Acquired loans	34,870	49,350
Lease exit obligation	2,626	1,747
Unrealized losses on available-for-sale investment securities	3,002	1,815
Unrealized losses on held-to-maturity investment securities	7,724	8,120
Unrealized losses on hedges	5,685	3,638
Other, net	4,914	6,324
Total deferred tax assets	135,653	158,083
Deferred Tax Liabilities
Accretion on investment securities	(599)	(449)
Other real estate owned	(284)	(178)
Purchase accounting	(16,615)	(15,112)
FDIC indemnification asset	(2,565)	(6,909)
Loan servicing rights	(3,890)	(3,558)
Other, net	(1,716)	(2,530)
Total deferred tax liabilities	(25,669)	(28,736)
Net deferred tax assets	$ 109,984	$ 129,347