Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current [Abstract]
Federal	$ 15,762	$ 35,839	$ 30,492
State	5,977	6,599	5,628
Total Current	21,739	42,438	36,120
Deferred [Abstract]
Federal	2,281	3,850	3,994
State	416	(278)	278
Total Deferred	2,697	3,572	4,272
Total income tax expense	$ 24,436	$ 46,010	40,392
Components of income taxes [Abstract]
Federal statutory income tax rate	21.00%	35.00%
Adjustment for remeasurement of deferred tax assets and liabilities for corporate rate reduction	$ 0	$ 4,407	0
Tax benefit primarily related to changes in accounting method	5,500
Deferred tax assets [Abstract]
Allowance for loan losses	18,042	17,390
Deferred compensation	7,340	7,230
Postretirement benefit obligation	1,962	2,159
Fair value adjustments from acquisitions	663	919
Unrealized losses on securities	4,893	3,715
Accrued liabilities	913	769
Stock-based compensation expense	2,821	2,642
Other	1,008	711
Total deferred tax assets	37,642	35,535
Deferred tax liabilities [Abstract]
Pension benefits	10,782	12,439
Amortization of intangible assets	11,525	11,110
Premises and equipment, primarily due to accelerated depreciation	4,973	2,792
Other	1,567	1,901
Total deferred tax liabilities	28,847	28,242
Net deferred tax asset at year-end	8,795	7,293	9,690
Net deferred tax asset at beginning of year	7,293	9,690
Increase (decrease) in net deferred tax asset	1,502	(2,397)
Income tax reconciliation [Abstract]
Federal income tax at statutory rate	28,770	44,857	41,581
Tax exempt income	(1,456)	(2,303)	(2,205)
Net increase in cash surrender value of life insurance	(973)	(1,780)	(1,712)
Federal tax credit	(1,499)	(1,343)	(1,323)
State taxes, net of federal tax benefit	5,051	4,107	3,838
Federal tax reform (Tax Act)	0	4,407	0
Accounting method changes - tax rate change impact	(5,326)	0	0
Stock-based compensation, excess tax benefit	(456)	(1,619)	0
Other, net	325	(316)	213
Total income tax expense	24,436	46,010	40,392
Reconciliation of gross unrecognized tax benefits [Roll Forward]
Beginning balance	665	559
Additions for tax positions of prior years	27	0
Reduction for tax positions of prior years	(159)	(31)
Current period tax positions	108	137
Ending balance	641	665	$ 559
Amount that would affect the effective tax rate if recognized, gross of tax	$ 506	525
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
Accounting Standards Update 2016-09 [Member]
Components of income taxes [Abstract]
Tax benefit associated with equity-based compensation	$ 500	$ 1,800