Goodwill and Other Intangibles - Changes In Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 121,226	$ 139,987
Accumulated amortization	104,590	118,931
Net carrying amount	16,636	21,056
Core Deposit Intangible Assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	50,059	50,059
Accumulated amortization	49,267	48,746
Net carrying amount	792	1,313
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	71,167	89,928
Accumulated amortization	55,323	70,185
Net carrying amount	$ 15,844	$ 19,743