Condensed Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Revision of Prior Period, Accounting Standards Update, Adjustment	Additional Paid-in Capital	Retained Earnings	Retained Earnings Revision of Prior Period, Accounting Standards Update, Adjustment	Accumulated Other Comprehensive Income
Beginning Balances at Dec. 31, 2019	$ 656,023	$ (15,635)	$ 379,853	$ 269,738	$ (15,635)	$ 6,432
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,606			46,606
Other comprehensive income (loss), net of tax	16,846					16,846
Amortization of unearned compensation	457		457
Exercise of stock options	157		157
Stock option expense	105		105
Stock issued stock plans	1,244		1,244
Repurchase of outstanding stock	(19,636)		(19,636)
Cash dividends on common stock	(15,874)			(15,874)
Ending Balances at Sep. 30, 2020	670,293		362,180	284,835		23,278
Beginning Balances at Jun. 30, 2020	652,206		361,087	269,849		21,270
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,312			20,312
Other comprehensive income (loss), net of tax	2,008					2,008
Amortization of unearned compensation	335		335
Exercise of stock options	0		0
Stock option expense	28		28
Stock issued stock plans	730		730
Cash dividends on common stock	(5,326)			(5,326)
Ending Balances at Sep. 30, 2020	670,293		362,180	284,835		23,278
Beginning Balances at Dec. 31, 2020	692,216		362,945	301,419		27,852
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	65,666			65,666
Other comprehensive income (loss), net of tax	(20,207)					(20,207)
Amortization of unearned compensation	1,233		1,233
Exercise of stock options	769		769
Stock option expense	55		55
Stock issued stock plans	(1,347)		(1,347)
Repurchase of outstanding stock	(7,607)		(7,607)
Stock retirement plans	(4,094)		(4,094)
Cash dividends on common stock	(18,142)			(18,142)
Ending Balances at Sep. 30, 2021	708,542		351,954	348,943		7,645
Beginning Balances at Jun. 30, 2021	710,374		359,227	332,509		18,638
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,071			23,071
Other comprehensive income (loss), net of tax	(10,993)					(10,993)
Amortization of unearned compensation	449		449
Exercise of stock options	0		0
Stock option expense	13		13
Repurchase of outstanding stock	(7,607)		(7,607)
Stock retirement plans	(128)		(128)
Cash dividends on common stock	(6,637)			(6,637)
Ending Balances at Sep. 30, 2021	$ 708,542		$ 351,954	$ 348,943		$ 7,645