Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Allowance for loan losses	$ 27,748	$ 32,626
Net actuarial loss on defined benefit post-retirement benefit plans	12,626	12,160
Stock-based compensation	10,622	9,904
Bonus accrual	4,586	1,136
Net unrealized loss on securities available for sale and transferred securities	4,283	0
Deferred loan and lease origination fees	2,153	1,280
Alternative minimum tax carryforward	410	47,104
Other	4,351	4,241
Total gross deferred tax assets	66,779	108,451
Premises and equipment	(23,859)	(20,236)
Intangible assets	(10,726)	(8,781)
Defined benefit post-retirement benefit plans	(9,452)	(9,012)
Leases	(1,709)	(1,646)
Net unrealized gain on securities available for sale and transferred securities	0	(35,829)
Other	(1,257)	(1,229)
Total gross deferred tax liabilities	(47,003)	(76,733)
Deferred Tax Assets, Net	$ 19,776	$ 31,718