Changes In Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 124,655	$ 125,024
Accumulated Amortization	104,398	98,394
Net Carrying Amounts	20,257	26,630
Core deposit intangible assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	50,059	47,527
Accumulated Amortization	42,209	39,040
Net Carrying Amounts	7,850	8,487
Customer relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	71,342	74,243
Accumulated Amortization	58,935	56,352
Net Carrying Amounts	12,407	17,891
Other intangible assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,254	3,254
Accumulated Amortization	$ 3,254	3,002
Net Carrying Amounts		$ 252