Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current [Abstract]
Federal		$ 35,839	$ 30,492	$ 32,871
State		6,599	5,628	4,329
Current tax expense		42,438	36,120	37,200
Deferred [Abstract]
Federal		3,850	3,994	2,521
State		(278)	278	482
Deferred tax expense		3,572	4,272	3,003
Total income tax expense		$ 46,010	40,392	40,203
Income Tax Disclosure [Line Items]
Federal statutory income tax rate		35.00%
Deferred tax assets [Abstract]
Allowance for loan losses		$ 17,390	24,925
Deferred compensation		7,230	11,578
Postretirement benefit obligation		2,159	2,929
Fair value adjustments from acquisitions		919	1,883
Unrealized losses on securities		3,715	3,259
Accrued liabilities		769	1,775
Stock-based compensation expense		2,642	4,817
Other		711	1,148
Total deferred tax assets		35,535	52,314
Deferred tax liabilities [Abstract]
Pension benefits		12,439	17,303
Amortization of intangible assets		11,110	17,557
Premises and equipment, primarily due to accelerated depreciation		2,792	4,375
Deferred loan costs		634	1,759
Cash flow hedge		877	1,129
Other		390	501
Total deferred tax liabilities		28,242	42,624
Net deferred tax asset at year-end		7,293	9,690	14,940
Net deferred tax asset at beginning of year	$ 7,293	9,690	14,940
(Decrease) in net deferred tax asset		(2,397)	(5,250)
Income tax reconciliation [Abstract]
Federal income tax at statutory rate		44,857	41,581	40,820
Tax exempt income		(2,303)	(2,205)	(2,037)
Net increase in cash surrender value of life insurance		(1,780)	(1,712)	(1,373)
Federal tax credits		(1,343)	(1,323)	(939)
State taxes, net of federal tax benefit		4,107	3,838	3,127
Federal tax reform (Tax Act)		4,407	0	0
Stock-based compensation, excess tax benefit		(1,619)	0	0
Other, net		(316)	213	605
Total income tax expense		46,010	40,392	40,203
Reconciliation of gross unrecognized tax benefits [Roll Forward]
Beginning balance	$ 665	559	0
Additions for tax positions of prior years		0	425
Reduction for tax positions of prior years		(31)	0
Current period tax positions		137	134
Ending balance		665	559	$ 0
Amount that would affect the effective tax rate if recognized, gross of tax		525	$ 363
Accounting Standards Update 2016-09 [Member]
Income Tax Disclosure [Line Items]
Tax benefit associated with equity-based compensation		$ 1,800
Plan [Member]
Income Tax Disclosure [Line Items]
Federal statutory income tax rate	21.00%
New York State [Member]
Income Tax Examination [Line Items]
Open tax year		2013