Goodwill and Other Intangibles - Changes In Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 139,987	$ 140,011
Accumulated amortization	115,806	112,414
Net carrying amount	24,181	27,597
Core Deposit Intangible Assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	50,059	50,059
Accumulated amortization	48,031	47,140
Net carrying amount	2,028	2,919
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	89,928	89,952
Accumulated amortization	67,775	65,274
Net carrying amount	$ 22,153	$ 24,678