CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common  Stock	Paid In  Capital	Retained  Earnings	Treasury  Stock	Accumulated Other Comprehensive Income (Loss)	Impact of CECL adoption	Impact of CECL adoption Retained  Earnings	Impact of CECL adoption Accumulated Other Comprehensive Income (Loss)	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, 2017	$ 754,140	$ 47,253	$ 757,439	$ 32,851	$ (47,105)	$ (36,298)	$ 0	$ (85)	$ 85	$ 754,140	$ 47,253	$ 757,439	$ 32,766	$ (47,105)	$ (36,213)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,138			74,138
Other comprehensive income (loss)	(14,015)					(14,015)
Issuance of common stock for dividend reinvestment plan	1,478	54	1,424
Purchase of common stock	(47,193)				(47,193)
Stock compensation expense	2,317		2,317
Net issuance of common stock under employee stock plan	2,405	0	1,290	(128)	1,243
Cash dividends paid on common stock	(41,979)			(41,979)
Ending balance, net of tax at Dec. 31, 2018	731,291	47,307	762,470	64,797	(93,055)	(50,228)	(16,452)	(16,452)		714,839	47,307	762,470	48,345	(93,055)	(50,228)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,554			74,554
Other comprehensive income (loss)	54,464					54,464
Issuance of common stock for dividend reinvestment plan	1,445	53	1,392
Purchase of common stock	(2,181)				(2,181)
Stock compensation expense	2,388		2,388
Net issuance of common stock under employee stock plan	1,592	0	468	(104)	1,228
Cash dividends paid on common stock	(42,521)			(42,521)
Ending 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	82,153			82,153
Other comprehensive income (loss)	64,844					64,844
Issuance of common stock for dividend reinvestment plan	1,424	59	1,365
Purchase of common stock	(30,989)				(30,989)
Stock compensation expense	3,020		3,020
Net issuance of common stock under employee stock plan	1,299	0	408	(185)	1,076
Cash dividends paid on common stock	(43,204)			(43,204)
Ending balance, net of tax at Dec. 31, 2020	$ 875,297	$ 47,419	$ 771,511	$ 111,208	$ (123,921)	$ 69,080