CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock Shares Outstanding [Member]	Common Stock Amount Issued [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss)/Income [Member]	Treasury Stock [Member]	Deferred Compensation Arrangements [Member]	Total
Balance at Dec. 31, 2018		$ 51,577	$ 911,748	$ 795,563	$ (45,305)	$ (11,528)	$ 11,728	$ 1,713,783
Balance (in shares) at Dec. 31, 2018	51,257,824
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				169,063				169,063
Other comprehensive income (loss), net of tax					35,079			35,079
Cash dividends declared:
Common				(81,775)				(81,775)
Common stock activity under employee stock ownership plans		398	6,517					6,915
Common stock activity under employee stock ownership plans (in shares)	397,887
Stock-based compensation			5,285					5,285
Distribution of stock under deferred compensation arrangements			1,064			830	(1,894)	0
Distribution of stock under deferred compensation arrangements (in shares)	32,431
Treasury stock issued to benefit plans, net			2,723			4,161		6,884
Treasury stock issued to benefit plans, net (in shares)	110,357
Treasury stock purchased						(286)	286	0
Treasury stock purchased (in shares)	(4,576)
Balance at Dec. 31, 2019		51,975	927,337	882,851	(10,226)	(6,823)	10,120	1,855,234
Balance (in shares) at Dec. 31, 2019	51,793,923
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				164,676				164,676
Other comprehensive income (loss), net of tax					72,303			72,303
Cumulative effect of change in accounting principle - ASC 326				1,140				1,140
Cash dividends declared:
Common				(88,484)				(88,484)
Common stock activity under employee stock ownership plans		417	15,375					15,792
Common stock activity under employee stock ownership plans (in shares)	416,614
Stock-based compensation			6,419					6,419
Stock issued for acquisition		1,363	75,579					76,942
Stock issued for acquisition (in shares)	1,363,259
Distribution of stock under deferred compensation arrangements			415			849	(1,264)	0
Distribution of stock under deferred compensation arrangements (in shares)	22,497
Treasury stock issued to benefit plans, net			38			47		85
Treasury stock issued to benefit plans, net (in shares)	1,240
Treasury stock purchased						(271)	271	0
Treasury stock purchased (in shares)	(4,406)
Balance at Dec. 31, 2020		53,755	1,025,163	960,183	62,077	(6,198)	9,127	2,104,107
Balance (in shares) at Dec. 31, 2020	53,593,127
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				189,694				189,694
Other comprehensive income (loss), net of tax					(112,704)			(112,704)
Cash dividends declared:
Common				(91,591)				(91,591)
Common stock activity under employee stock ownership plans		337	9,484					9,821
Common stock activity under employee stock ownership plans (in shares)	337,822
Stock-based compensation			6,334					6,334
Distribution of stock under deferred compensation arrangements			323			694	(1,017)	0
Distribution of stock under deferred compensation arrangements (in shares)	18,089
Treasury stock purchased						(5,106)	252	(4,854)
Treasury stock purchased (in shares)	(70,991)
Balance at Dec. 31, 2021		$ 54,092	$ 1,041,304	$ 1,058,286	$ (50,627)	$ (10,610)	$ 8,362	$ 2,100,807
Balance (in shares) at Dec. 31, 2021	53,878,047