Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Allowance for loan losses	$ 47,551	$ 34,840
Net actuarial loss on defined benefit post-retirement benefit plans	25,172	26,263
Stock-based compensation	21,246	18,839
Alternative minimum tax carryforward	10,934	0
Bonus accrual	5,832	6,118
Gain on sale of assets	2,044	2,139
Transaction costs	1,716	1,794
Partnerships	1,271	1,911
Other	4,447	5,272
Total gross deferred tax assets	120,213	97,176
Net unrealized gain on securities available for sale and effective cash flow hedging derivatives	(86,484)	(102,626)
Premises and equipment	(23,038)	(20,039)
Defined benefit post-retirement benefit plans	(14,089)	(15,010)
Intangible assets	(8,940)	(6,143)
Leases	(4,491)	(4,952)
Section 481(a) change in accounting method (tangible property)	(3,387)	0
Prepaid expenses	(1,702)	(1,639)
Reserve for medical insurance	(211)	(3,017)
Other	(352)	(341)
Total gross deferred tax liabilities	(142,694)	(153,767)
Deferred Tax Liabilities, Net	$ (22,481)	$ (56,591)