Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current [Abstract]
Federal	$ 30,492	$ 32,871	$ 26,059
State	5,628	4,329	2,823
Current tax expense	36,120	37,200	28,882
Deferred [Abstract]
Federal	3,994	2,521	6,648
State	278	482	1,699
Deferred tax expense	4,272	3,003	8,347
Total income tax expense	40,392	40,203	37,229
Income tax recorded to stockholders' equity	400	3,400	(1,100)
Deferred tax assets [Abstract]
Allowance for loan losses	24,925	24,090
Deferred compensation	11,578	10,023
Postretirement benefit obligation	2,929	2,988
Fair value adjustments from acquisitions	1,883	2,543
Unrealized losses on securities	3,259	589
Accrued liabilities	1,775	2,889
Stock-based compensation expense	4,817	5,394
Equipment leasing	256	476
Other	892	1,477
Total deferred tax assets	52,314	50,469
Deferred tax liabilities [Abstract]
Pension benefits	17,303	11,908
Intangible amortization	17,557	19,082
Premises and equipment, primarily due to accelerated depreciation	4,375	2,444
Deferred loan costs	1,759	1,591
Cash flow hedge	1,129	0
Other	501	504
Total deferred tax liabilities	42,624	35,529
Net deferred tax asset at year-end	9,690	14,940	14,517
Net deferred tax asset (liability) at beginning of year	14,940	14,517
(Decrease) increase in net deferred tax asset	$ (5,250)	423
Federal statutory income tax rate	35.00%
Income tax reconciliation [Abstract]
Federal income tax at statutory rate	$ 41,581	40,820	39,306
Tax exempt income	(2,205)	(2,037)	(2,250)
Net increase in CSV of life insurance	(1,712)	(1,373)	(1,734)
Federal tax credits	(1,323)	(939)	(880)
State taxes, net of federal tax benefit	3,838	3,127	2,939
Other, net	213	605	(152)
Total income tax expense	40,392	40,203	$ 37,229
Reconciliation of gross unrecognized tax benefits [Roll Forward]
Beginning balance	0
Additions for tax positions of prior years	425
Current period tax positions	134
Ending balance	559	$ 0
Amount that would affect the effective tax rate if recognized	$ 363
New York State [Member] | Minimum [Member]
Income Tax Examination [Line Items]
Tax years under audit	2011
New York State [Member] | Maximum [Member]
Income Tax Examination [Line Items]
Tax years under audit	2013