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)
Beginning balance (in shares) at Dec. 31, 2018		51,361
Beginning balance at Dec. 31, 2018	$ 864,267	$ 5,136	$ 778,501	$ 97,074	$ (3,384)	$ (13,060)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	31,548			22,705		8,843
Stock based compensation expense	2,129		2,129
Common stock transactions related to stock based employee benefit plans (in shares)		49
Common stock transactions related to stock based employee benefit plans	(1,584)	$ 5	(14)		(1,575)
Common stock issued for stock options (in shares)		4
Common stock issued for stock options	64		64
Increase (decrease) in shares during period (in shares)		53
Increase (decrease) in stockholders' equity during period	32,157	$ 5	2,179	22,705	(1,575)	8,843
Ending balance (in shares) at Mar. 31, 2019		51,414
Ending balance at Mar. 31, 2019	896,424	$ 5,141	780,680	119,779	(4,959)	(4,217)
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
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