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	1,003			709		294
Stock based compensation expense	2,000		2,000
Common stock transactions related to stock based employee benefit plans (in shares)		115
Common stock transactions related to stock based employee benefit plans	(1,410)	$ 12	(32)		(1,390)
Common stock issued for stock options (in shares)		37
Common stock issued for stock options	400	$ 4	396
Issuance of common stock, pursuant to acquisition (in shares)		1,043
Issuance of common stock, pursuant to acquisition	21,031	$ 104	20,927
Increase (decrease) in shares during period (in shares)		1,195
Increase (decrease) in stockholders' equity during period	6,148	$ 120	23,291	(16,167)	(1,390)	294
Ending balance (in shares) at Mar. 31, 2020		52,709
Ending balance at Mar. 31, 2020	991,787	$ 5,271	809,533	179,646	(7,422)	4,759
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	22,754			33,719		(10,965)
Stock based compensation expense	1,759		1,759
Common stock transactions related to stock based employee benefit plans (in shares)		20
Common stock transactions related to stock based employee benefit plans	(406)	$ 2			(408)
Common stock issued for stock options (in shares)		31
Common stock issued for stock options	840	$ 3	837
Increase (decrease) in shares during period (in shares)		51
Increase (decrease) in stockholders' equity during period	24,947	$ 5	2,596	33,719	(408)	(10,965)
Ending balance (in shares) at Mar. 31, 2021		55,294
Ending balance at Mar. 31, 2021	$ 1,155,349	$ 5,529	$ 858,688	$ 290,420	$ (8,693)	$ 9,405