Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current [Abstract]
Federal	$ 28,475	$ 15,762	$ 35,839
State	7,653	5,977	6,599
Total Current	36,128	21,739	42,438
Deferred [Abstract]
Federal	(1,379)	2,281	3,850
State	(338)	416	(278)
Total Deferred	(1,717)	2,697	3,572
Total income tax expense	$ 34,411	24,436	$ 46,010
Components of income taxes [Abstract]
Federal statutory income tax rate	21.00%		35.00%
Non-cash adjustment for remeasurement of deferred tax assets and liabilities for corporate rate reduction	$ 0	0	$ 4,407
Tax benefit primarily related to changes in accounting method		5,500
Deferred tax assets [Abstract]
Allowance for loan losses	18,535	18,042
Lease liability	9,331	0
Deferred compensation	8,336	7,340
Postretirement benefit obligation	1,631	1,962
Fair value adjustments from acquisitions	422	663
Unrealized losses on securities	0	4,893
Accrued liabilities	1,176	913
Stock-based compensation expense	3,032	2,821
Other	1,498	1,008
Total deferred tax assets	43,961	37,642
Deferred tax liabilities [Abstract]
Pension benefits	13,014	10,782
Lease right-of-use asset	9,259	0
Amortization of intangible assets	12,202	11,525
Premises and equipment, primarily due to accelerated depreciation	5,137	4,973
Unrealized gain on securities	1,770	0
Other	45	1,567
Total deferred tax liabilities	41,427	28,847
Net deferred tax asset at year-end	2,534	8,795	7,293
Net deferred tax asset at beginning of year	8,795	7,293
(Decrease) increase in net deferred tax asset	(6,261)	1,502
Income tax reconciliation [Abstract]
Federal income tax at statutory rate	32,641	28,770	44,857
Tax exempt income	(1,233)	(1,456)	(2,303)
Net increase in cash surrender value of life insurance	(927)	(973)	(1,780)
Federal tax credit	(1,458)	(1,499)	(1,343)
State taxes, net of federal tax benefit	5,773	5,051	4,107
Federal tax reform (Tax Act)	0	0	4,407
Accounting method changes - tax rate change impact	0	(5,326)	0
Stock-based compensation, excess tax benefit	(342)	(456)	(1,619)
Other, net	(43)	325	(316)
Total income tax expense	34,411	24,436	46,010
Reconciliation of gross unrecognized tax benefits [Roll Forward]
Beginning balance	641	665
Additions for tax positions of prior years	26	27
Reduction for tax positions of prior years	0	(159)
Current period tax positions	112	108
Ending balance	779	641	$ 665
Amount that would affect the effective tax rate if recognized, gross of tax	$ 615	$ 506
State and Local Jurisdiction [Member] | New York State Division of Taxation and Finance [Member]
Income Tax Examination [Abstract]
Tax years under examination	2014 2015 2016