CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Cumulative change in accounting principle upon adoption of new accounting pronouncement	Cumulative change in accounting principle upon adoption of new accounting pronouncement Retained Earnings
Beginning balance (in shares) at Dec. 31, 2019		51,514
Beginning balance at Dec. 31, 2019	$ 985,639	$ 5,151	$ 786,242	$ 195,813	$ (6,032)	$ 4,465	$ (16,876)	$ (16,876)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	63,175			48,417		14,758
Stock based compensation (in shares)		39
Stock based compensation expense	5,471		5,471
Common stock transactions related to stock based employee benefit plans (in shares)		395
Common stock transactions related to stock based employee benefit plans	(1,918)	$ 44	(53)		(1,909)
Common stock issued for stock options (in shares)		58
Common stock issued for stock options	698	$ 6	692
Issuance of common stock, pursuant to acquisition (in shares)		3,163
Issuance of common stock, pursuant to acquisition	62,152	$ 316	61,836
Increase (decrease) in shares during period (in shares)		3,655
Increase (decrease) in stockholders' equity during period	112,702	$ 366	67,946	31,541	(1,909)	14,758
Ending balance (in shares) at Sep. 30, 2020		55,169
Ending balance at Sep. 30, 2020	1,098,341	$ 5,517	854,188	227,354	(7,941)	19,223
Beginning balance (in shares) at Jun. 30, 2020		52,991
Beginning balance at Jun. 30, 2020	1,030,603	$ 5,299	811,321	204,726	(8,037)	17,294
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	24,557			22,628		1,929
Stock based compensation (in shares)		39
Stock based compensation expense	1,948		1,948
Common stock transactions related to stock based employee benefit plans (in shares)		18
Common stock transactions related to stock based employee benefit plans	96	$ 6	(6)		96
Common stock issued for stock options (in shares)		1
Common stock issued for stock options	16		16
Issuance of common stock, pursuant to acquisition (in shares)		2,120
Issuance of common stock, pursuant to acquisition	41,121	$ 212	40,909
Increase (decrease) in shares during period (in shares)		2,178
Increase (decrease) in stockholders' equity during period	67,738	$ 218	42,867	22,628	96	1,929
Ending balance (in shares) at Sep. 30, 2020		55,169
Ending balance at Sep. 30, 2020	1,098,341	$ 5,517	854,188	227,354	(7,941)	19,223
Beginning balance (in shares) at Dec. 31, 2020		55,243
Beginning balance at Dec. 31, 2020	1,130,402	$ 5,524	856,092	256,701	(8,285)	20,370
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	72,972			88,073		(15,101)
Stock based compensation (in shares)		23
Stock based compensation expense	6,620		6,620
Common stock transactions related to stock based employee benefit plans (in shares)		139
Common stock transactions related to stock based employee benefit plans	(1,884)	$ 17	(40)		(1,861)
Common stock issued for stock options (in shares)		257
Common stock issued for stock options	5,172	$ 25	5,147
Issuance of common stock, pursuant to acquisition (in shares)		2,687
Issuance of common stock, pursuant to acquisition	86,487	$ 269	86,218
Conversion of options, pursuant to acquisition	5,607		5,607
Dividends on common stock	(14,856)			(14,856)
Increase (decrease) in shares during period (in shares)		3,106
Increase (decrease) in stockholders' equity during period	160,118	$ 311	103,552	73,217	(1,861)	(15,101)
Ending balance (in shares) at Sep. 30, 2021		58,349
Ending balance at Sep. 30, 2021	1,290,520	$ 5,835	959,644	329,918	(10,146)	5,269
Beginning balance (in shares) at Jun. 30, 2021		55,436
Beginning balance at Jun. 30, 2021	1,182,347	$ 5,544	862,598	314,584	(10,180)	9,801
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	18,412			22,944		(4,532)
Stock based compensation (in shares)		23
Stock based compensation expense	2,358		2,358
Common stock transactions related to stock based employee benefit plans (in shares)		25
Common stock transactions related to stock based employee benefit plans	17	$ 5	(22)		34
Common stock issued for stock options (in shares)		178
Common stock issued for stock options	2,902	$ 17	2,885
Issuance of common stock, pursuant to acquisition (in shares)		2,687
Issuance of common stock, pursuant to acquisition	86,487	$ 269	86,218
Conversion of options, pursuant to acquisition	5,607		5,607
Dividends on common stock	(7,610)			(7,610)
Increase (decrease) in shares during period (in shares)		2,913
Increase (decrease) in stockholders' equity during period	108,173	$ 291	97,046	15,334	34	(4,532)
Ending balance (in shares) at Sep. 30, 2021		58,349
Ending balance at Sep. 30, 2021	$ 1,290,520	$ 5,835	$ 959,644	$ 329,918	$ (10,146)	$ 5,269