Goodwill and Other Intangibles - Changes In Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 139,987	$ 140,011
Accumulated amortization	118,931	112,414
Net carrying amount	21,056	27,597
Core Deposit Intangible Assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	50,059	50,059
Accumulated amortization	48,746	47,140
Net carrying amount	1,313	2,919
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	89,928	89,952
Accumulated amortization	70,185	65,274
Net carrying amount	$ 19,743	$ 24,678