CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Common stock, shares outstanding at Dec. 31, 2019		17,363,000
Shareholders' equity at Dec. 31, 2019	$ 503,492	$ 1,085	$ 123,281	$ 390,363	$ (11,237)	$ 0
Shareholders' equity (Accounting Standards Update 2016-13) at Dec. 31, 2019	(6,108)			(6,108)
Net income	51,263			51,263
Total other comprehensive income (loss), net of tax	7,834				7,834
Cash dividends declared	(26,745)			(26,745)
Share-based compensation	2,696		2,696
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, shares		22,000
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, value	(417)	$ 0	(1,209)			792
Treasury stock purchased under 2019 Stock Repurchase Program, shares acquired		(125,000)
Treasury stock purchased under 2019 Stock Repurchase Program, amount acquired	(4,322)					(4,322)
Common stock, shares outstanding at Sep. 30, 2020		17,260,000
Shareholders' equity at Sep. 30, 2020	527,693	$ 1,085	124,768	408,773	(3,403)	(3,530)
Common stock, shares outstanding at Jun. 30, 2020		17,260,000
Shareholders' equity at Jun. 30, 2020	520,163	$ 1,085	123,684	399,386	(462)	(3,530)
Net income	18,322			18,322
Total other comprehensive income (loss), net of tax	(2,941)				(2,941)
Cash dividends declared	(8,935)			(8,935)
Share-based compensation	1,083		1,083
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, shares		0
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, value	1	$ 0	1			0
Common stock, shares outstanding at Sep. 30, 2020		17,260,000
Shareholders' equity at Sep. 30, 2020	$ 527,693	$ 1,085	124,768	408,773	(3,403)	(3,530)
Common stock, shares outstanding at Dec. 31, 2020	17,265,337	17,265,000
Shareholders' equity at Dec. 31, 2020	$ 534,195	$ 1,085	125,610	418,246	(7,391)	(3,355)
Net income	56,682			56,682
Total other comprehensive income (loss), net of tax	(10,737)				(10,737)
Cash dividends declared	(27,362)			(27,362)
Share-based compensation	2,705		2,705
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, shares		55,000
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, value	$ (165)	$ 0	(2,050)			1,885
Common stock, shares outstanding at Sep. 30, 2021	17,320,449	17,320,000
Shareholders' equity at Sep. 30, 2021	$ 555,318	$ 1,085	126,265	447,566	(18,128)	(1,470)
Common stock, shares outstanding at Jun. 30, 2021		17,320,000
Shareholders' equity at Jun. 30, 2021	547,856	$ 1,085	125,442	437,927	(15,128)	(1,470)
Net income	18,751			18,751
Total other comprehensive income (loss), net of tax	(3,000)				(3,000)
Cash dividends declared	(9,112)			(9,112)
Share-based compensation	823		823
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, shares		0
Exercise of stock options and issuance of other compensation-related equity awards, net of awards surrendered, value	$ 0	$ 0	0			0
Common stock, shares outstanding at Sep. 30, 2021	17,320,449	17,320,000
Shareholders' equity at Sep. 30, 2021	$ 555,318	$ 1,085	$ 126,265	$ 447,566	$ (18,128)	$ (1,470)