CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Paid In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Cumulative effect of accounting change	Cumulative effect of accounting change Retained Earnings	Adjusted beginning balance	Adjusted beginning balance Common Stock	Adjusted beginning balance Paid In Capital	Adjusted beginning balance Retained Earnings	Adjusted beginning balance Treasury Stock	Adjusted beginning balance Accumulated Other Comprehensive Income (Loss)
Beginning balance, net of tax at Dec. 31, 2019	$ 804,580	$ 47,360	$ 766,718	$ 80,274	$ (94,008)	$ 4,236	$ (7,830)	$ (7,830)	$ 796,750	$ 47,360	$ 766,718	$ 72,444	$ (94,008)	$ 4,236
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,953			3,953
Other comprehensive (loss) income	29,303					29,303
Issuance of common stock for dividend reinvestment plan	347	13	334
Purchase of common stock	(25,842)				(25,842)
Stock compensation expense	695		695
Net issuance of common stock under employee stock plans	1,088		693	(40)	435
Cash dividends paid on common stock	(10,494)			(10,494)
Ending balance, net of tax at Mar. 31, 2020	795,800	47,373	768,440	65,863	(119,415)	33,539
Beginning balance, net of tax at Dec. 31, 2019	804,580	47,360	766,718	80,274	(94,008)	4,236	$ (7,830)	$ (7,830)	$ 796,750	$ 47,360	$ 766,718	$ 72,444	$ (94,008)	$ 4,236
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	52,581
Other comprehensive (loss) income	42,035
Ending balance, net of tax at Sep. 30, 2020	839,148	47,402	770,639	93,916	(119,080)	46,271
Beginning balance, net of tax at Mar. 31, 2020	795,800	47,373	768,440	65,863	(119,415)	33,539
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,554			21,554
Other comprehensive (loss) income	9,472					9,472
Issuance of common stock for dividend reinvestment plan	336	14	322
Stock compensation expense	772		772
Net issuance of common stock under employee stock plans	(96)		(127)	(50)	81
Cash dividends paid on common stock	(10,233)			(10,233)
Ending balance, net of tax at Jun. 30, 2020	817,605	47,387	769,407	77,134	(119,334)	43,011
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27,074			27,074
Other comprehensive (loss) income	3,260					3,260
Issuance of common stock for dividend reinvestment plan	337	15	322
Stock compensation expense	786		786
Net issuance of common stock under employee stock plans	331		124	(47)	254
Cash dividends paid on common stock	(10,245)			(10,245)
Ending balance, net of tax at Sep. 30, 2020	839,148	47,402	770,639	93,916	(119,080)	46,271
Beginning balance, net of tax at Dec. 31, 2020	875,297	47,419	771,511	111,208	(123,921)	69,080
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,091			34,091
Other comprehensive (loss) income	(29,494)					(29,494)
Issuance of common stock for dividend reinvestment plan	332	11	321
Purchase of common stock	(15,213)				(15,213)
Stock compensation expense	674		674
Net issuance of common stock under employee stock plans	3,386		2,309	(41)	1,118
Cash dividends paid on common stock	(10,476)			(10,476)
Ending balance, net of tax at Mar. 31, 2021	858,597	47,430	774,815	134,782	(138,016)	39,586
Beginning balance, net of tax at Dec. 31, 2020	875,297	47,419	771,511	111,208	(123,921)	69,080
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	84,714
Other comprehensive (loss) income	(25,106)
Ending balance, net of tax at Sep. 30, 2021	877,866	47,450	778,600	163,809	(155,967)	43,974
Beginning balance, net of tax at Mar. 31, 2021	858,597	47,430	774,815	134,782	(138,016)	39,586
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,317			21,317
Other comprehensive (loss) income	25,301					25,301
Issuance of common stock for dividend reinvestment plan	330	9	321
Purchase of common stock	(3,497)				(3,497)
Stock compensation expense	686		686
Net issuance of common stock under employee stock plans	2,441		1,591	(47)	897
Cash dividends paid on common stock	(10,775)			(10,775)
Ending balance, net of tax at Jun. 30, 2021	894,400	47,439	777,413	145,277	(140,616)	64,887
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,306			29,306
Other comprehensive (loss) income	(20,913)					(20,913)
Issuance of common stock for dividend reinvestment plan	324	11	313
Purchase of common stock	(15,438)				(15,438)
Stock compensation expense	829		829
Net issuance of common stock under employee stock plans	64		45	(68)	87
Cash dividends paid on common stock	(10,706)			(10,706)
Ending balance, net of tax at Sep. 30, 2021	$ 877,866	$ 47,450	$ 778,600	$ 163,809	$ (155,967)	$ 43,974