CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect Adjustment	Common Stock	Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect Adjustment	Treasury Stock	Accumulated Other Comprehensive Income (Loss), Net
Beginning balance (in shares) at Dec. 31, 2017			46,918
Beginning balance at Dec. 31, 2017	$ 689,664		$ 4,693	$ 661,632	$ 29,914		$ (2,359)	$ (4,216)
Comprehensive income	58,316				67,275			(8,959)
Reclassification of disproportionate tax effects upon adoption of new accounting pronouncement	0				(115)			115
Stock based compensation expense (in shares)			32
Stock based compensation expense	7,823			7,823
Common stock issued for stock based employee benefit plans (in shares)			43
Common stock issued for stock based employee benefit plans	(1,031)			(6)			(1,025)
Common stock issued for stock options (in shares)			368
Common stock issued for stock options	2,009		$ 43	1,966
Issuance of common stock, pursuant to acquisition (in shares)			4,000
Issuance of common stock, pursuant to acquisition	107,486		$ 400	107,086
Ending balance (in shares) at Dec. 31, 2018			51,361
Ending balance at Dec. 31, 2018	864,267		$ 5,136	778,501	97,074		(3,384)	(13,060)
Comprehensive income	116,264				98,739			17,525
Stock based compensation expense (in shares)			30
Stock based compensation expense	7,244			7,244
Common stock issued for stock based employee benefit plans (in shares)			94
Common stock issued for stock based employee benefit plans	(2,668)		$ 12	(32)			(2,648)
Common stock issued for stock options (in shares)			29
Common stock issued for stock options	428		$ 3	425
Other	104			104
Ending balance (in shares) at Dec. 31, 2019			51,514
Ending balance at Dec. 31, 2019	985,639	$ (16,876)	$ 5,151	786,242	195,813	$ (16,876)	(6,032)	4,465
Comprehensive income	93,669				77,764			15,905
Stock based compensation expense (in shares)			39
Stock based compensation expense	7,304			7,304
Common stock issued for stock based employee benefit plans (in shares)			465
Common stock issued for stock based employee benefit plans	(2,252)		$ 51	(50)			(2,253)
Common stock issued for stock options (in shares)			62
Common stock issued for stock options	766		$ 6	760
Issuance of common stock, net of related expenses (in shares)			3,163
Issuance of common stock, pursuant to acquisitions	62,152		$ 316	61,836
Ending balance (in shares) at Dec. 31, 2020			55,243
Ending balance at Dec. 31, 2020	$ 1,130,402		$ 5,524	$ 856,092	$ 256,701		$ (8,285)	$ 20,370