Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Shares	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2020	$ 575,673	$ 422,536	$ 190,691	$ 1,336	$ (38,890)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	25,566		25,566
Other comprehensive income (loss), net of tax	(3,558)			(3,558)
Cash dividends declared	(13,898)		(13,898)
Reissuance of treasury stock for common share awards	0	(2,172)			2,172
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	74				74
Repurchase of treasury stock in connection with employee incentive program and compensation plan for Boards of Directors	(998)				(998)
Common shares issued under dividend reinvestment plan	378	378
Common shares issued under compensation plan for Boards of Directors	249	65			184
Common shares issued under employee stock purchase plan	235	61			174
Stock-based compensation	1,784	1,784
Ending balance at Jun. 30, 2021	585,505	422,652	202,359	(2,222)	(37,284)
Beginning balance at Mar. 31, 2021	578,893	422,370	199,321	(4,962)	(37,836)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	10,103		10,103
Other comprehensive income (loss), net of tax	2,740			2,740
Cash dividends declared	(7,065)		(7,065)
Reissuance of treasury stock for common share awards	0	(432)			432
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	72				72
Repurchase of treasury stock in connection with employee incentive program and compensation plan for Boards of Directors	(87)				(87)
Common shares issued under dividend reinvestment plan	90	90
Common shares issued under compensation plan for Boards of Directors	55	12			43
Common shares issued under employee stock purchase plan	118	26			92
Stock-based compensation	586	586
Ending balance at Jun. 30, 2021	585,505	422,652	202,359	(2,222)	(37,284)
Beginning balance at Dec. 31, 2021	845,025	686,282	207,076	(11,619)	(36,714)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,465		48,465
Other comprehensive income (loss), net of tax	(81,740)			(81,740)
Cash dividends declared	(20,933)		(20,933)
Reissuance of treasury stock for common share awards	0	(4,725)			4,725
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	78				78
Repurchase of treasury stock in connection with employee incentive program and compensation plan for Boards of Directors	(1,436)				(1,436)
Common shares repurchased under share repurchase program then in effect	(5,987)				(5,987)
Common shares issued under dividend reinvestment plan	601	601
Common shares issued under compensation plan for Boards of Directors	252	44			208
Common shares issued under employee stock purchase plan	346	61			285
Stock-based compensation	2,153	2,153
Ending balance at Jun. 30, 2022	786,824	684,416	234,608	(93,359)	(38,841)
Beginning balance at Mar. 31, 2022	808,341	684,243	220,477	(62,666)	(33,713)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,888		24,888
Other comprehensive income (loss), net of tax	(30,693)			(30,693)
Cash dividends declared	(10,757)		(10,757)
Reissuance of treasury stock for common share awards	0	(727)			727
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	78				78
Repurchase of treasury stock in connection with employee incentive program and compensation plan for Boards of Directors	(206)				(206)
Common shares repurchased under share repurchase program then in effect	(5,987)				(5,987)
Common shares issued under dividend reinvestment plan	296	296
Common shares issued under compensation plan for Boards of Directors	128	13			115
Common shares issued under employee stock purchase plan	160	15			145
Stock-based compensation	576	576
Ending balance at Jun. 30, 2022	$ 786,824	$ 684,416	$ 234,608	$ (93,359)	$ (38,841)