Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Allowance for loan losses	$ 32,626	$ 53,566
Alternative minimum tax carryforward	47,104	30,384
Net actuarial loss on defined benefit post-retirement benefit plans	12,160	21,956
Stock-based compensation	9,904	18,140
Bonus accrual	1,136	7,035
Gain on sale of assets	883	2,485
Transaction costs	875	1,587
Other	3,996	4,449
Total gross deferred tax assets	108,684	139,602
Premises and equipment	(20,236)	(33,777)
Defined benefit post-retirement benefit plans	(9,012)	(14,828)
Intangible assets	(9,014)	(11,697)
Net unrealized gain on securities available for sale and transferred securities	(35,829)	(8,699)
Leases	(1,646)	(3,042)
Section 481(a) change in accounting method (tangible property)	0	(1,694)
Prepaid expenses	(996)	(1,743)
Other	(233)	(436)
Total gross deferred tax liabilities	(76,966)	(75,916)
Deferred Tax Assets, Net	$ 31,718	$ 63,686