Income Taxes - Company's Net Deferred Tax Asset Recorded in Other Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Allowance for losses and reserve for unfunded commitments	$ 28,159	$ 9,871
Deferred compensation	1,786	2,342
Accrued pension liability	383	3,309
Other accrued expenses	1,537	1,678
Additional unfunded status of the supplemental retirement plans	13,275	9,868
Operating lease liability	8,270	8,142
State taxes	2,870	2,441
Share based compensation	837	803
Nonaccrual interest	725	649
Acquisition cost basis	2,372	4,556
Unrealized loss on securities	0	0
Tax credits	513	576
Tax credit related to operating losses	1,131	1,578
Other	327	348
Total deferred tax assets	62,185	46,161
Deferred tax liabilities:
Securities income	(762)	(762)
Depreciation	(7,231)	(6,109)
Right of use asset	(8,232)	(8,242)
Merger related fixed asset valuations	(30)	(30)
Securities accretion	(702)	(560)
Mortgage servicing rights valuation	(1,490)	(1,813)
Unrealized gain on securities	(5,671)	(1,001)
Core deposit intangible	(4,812)	(6,453)
Junior subordinated debt	(1,553)	(1,672)
Prepaid expenses and other	(502)	(469)
Total deferred tax liability	(30,985)	(27,111)
Net deferred tax asset	$ 31,200	$ 19,050