Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($)		Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock Outstanding	Common Stock	Value of Shares Held in Rabbi Trust at Cost	Deferred Compensation and Other Retirement Benefit Obligations	Additional Paid in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income/(Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding				34,377,388
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method		$ (1,137,000)
Net income		51,653,000							$ 51,653,000
Other comprehensive income		33,676,000									$ 33,676,000
Cash dividends declared per common share (in dollars per share)									$ 0.92
Common dividend declared		(30,554,000)							$ (30,554,000)
Proceeds from exercise of stock options, net of cash paid				873
Stock based compensation		2,429,000						$ 2,429,000
Restricted stock awards issued, net of awards surrendered				49,292
Restricted stock awards issued, net of awards surrendered		(1,183,000)			$ 1,000			(1,184,000)
Shares issued under direct stock purchase plan				14,557
Shares issued under direct stock purchase plan		1,092,000			0			1,092,000
Stock Repurchased During Period, Shares				(1,500,000)
Stock Repurchased During Period, Value		(95,091,000)			(15,000)			(95,076,000)
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						$ 86,000	$ (86,000)
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Jun. 30, 2020		1,671,692,000			328,000	(4,649,000)	4,649,000	942,685,000	676,834,000		51,845,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method, net of tax.		817,000
Off-Balance Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)		(1,000,000.0)
Off-Balance Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal), net of tax.		736,000
Proceeds from exercise of stock options, net of cash paid		(26,000)			0			(26,000)
Common Stock, Shares, Outstanding				33,260,005
Net income		24,902,000							$ 24,902,000
Other comprehensive income		2,117,000									2,117,000
Cash dividends declared per common share (in dollars per share)									$ 0.46
Common dividend declared		(15,152,000)							$ (15,152,000)
Proceeds from exercise of stock options, net of cash paid				873
Stock Repurchased During Period, Value, as a result of Stock Options Exercised		(26,000)						(26,000)
Stock based compensation		1,579,000						1,579,000
Restricted stock awards issued, net of awards surrendered				6,761
Restricted stock awards issued, net of awards surrendered		(51,000)						(51,000)
Shares issued under direct stock purchase plan				7,548
Shares issued under direct stock purchase plan		532,000						532,000
Stock Repurchased During Period, Shares				(333,077)
Stock Repurchased During Period, Value		(21,865,000)			(3,000)			(21,862,000)
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(45,000)	45,000
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Jun. 30, 2020		$ 1,671,692,000			328,000	(4,649,000)	4,649,000	942,685,000	676,834,000		51,845,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding				32,942,110
Common Stock, Shares, Outstanding		32,965,692		32,965,692
Cumulative Effect of New Accounting Principle in Period of Adoption (Deprecated 2020-01-31)	[1]		$ 1,553,000							$ 1,553,000
Net income		$ 79,283,000							$ 79,283,000
Other comprehensive income		(11,128,000)									(11,128,000)
Cash dividends declared per common share (in dollars per share)									$ 0.96
Common dividend declared		(31,711,000)							$ (31,711,000)
Proceeds from exercise of stock options, net of cash paid				4,744
Stock Repurchased During Period, Value, as a result of Stock Options Exercised		(57,000)						(57,000)
Stock based compensation		2,760,000						2,760,000
Restricted stock awards issued, net of awards surrendered				54,558
Restricted stock awards issued, net of awards surrendered		(1,243,000)			1,000			(1,244,000)
Shares issued under direct stock purchase plan				12,865
Shares issued under direct stock purchase plan		1,033,000						1,033,000
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(50,000)	50,000
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Jun. 30, 2021		1,741,622,000			329,000	(3,116,000)	3,116,000	948,130,000	763,596,000		29,567,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding				33,024,882
Net income		37,572,000							$ 37,572,000
Other comprehensive income		2,410,000									2,410,000
Cash dividends declared per common share (in dollars per share)									$ 0.48
Common dividend declared		(15,859,000)							$ (15,859,000)
Stock based compensation		1,610,000						1,610,000
Restricted stock awards issued, net of awards surrendered				6,452
Restricted stock awards issued, net of awards surrendered		(23,000)						(23,000)
Shares issued under direct stock purchase plan				6,525
Shares issued under direct stock purchase plan		541,000						541,000
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(36,000)	36,000
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Jun. 30, 2021		$ 1,741,622,000			$ 329,000	$ (3,116,000)	$ 3,116,000	$ 948,130,000	$ 763,596,000		$ 29,567,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		33,037,859		33,037,859

[1] Represents adjustment needed to reflect the cumulative impact on retained earnings pursuant to the Company's adoption of Accounting Standards Update 2016-13. The adjustment presented includes $1.1 million ($817,000, net of tax) attributable to the change in accounting methodology for estimating the allowance for credit losses and $1.0 million ($736,000, net of tax) related to the reserve for unfunded commitments resulting from the Company's adoption of the standard. Amount shown in the table above is presented net of tax.