Changes In Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 121,911	$ 121,911
Accumulated amortization	108,235	106,908
Net carrying amount	13,676	15,003
Core deposit intangible assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	50,059	50,059
Accumulated amortization	45,615	44,998
Net carrying amount	4,444	5,061
Customer relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	71,852	71,852
Accumulated amortization	62,620	61,910
Net carrying amount	$ 9,232	$ 9,942