Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Stock in Rabbi Trust Assumed in Acquisition [Member]	Rabbi Trust Obligation [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Beginning balance at Dec. 31, 2016	$ 147,287	$ 225,921			$ (5,107)	$ 368,101
Beginning balance, shares at Dec. 31, 2016	20,845
Net income		7,555				7,555
Cash dividends declared		(1,973)				(1,973)
Equity issued pursuant to acquisitions	$ 114,478		(7,688)	7,688		114,478
Equity issued pursuant to acquisitions, shares	3,799
Stock option exercises	$ 45					45
Stock option exercises, shares	4
Stock-based compensation	$ 370					370
Stock-based compensation, shares	15
Other comprehensive income (loss)					885	885
Ending balance at Mar. 31, 2017	$ 262,180	231,503	(7,688)	7,688	(4,222)	$ 489,461
Ending balance, shares at Mar. 31, 2017	24,663					24,663,241
Beginning balance at Dec. 31, 2017	$ 432,794	264,331	(3,581)	3,581	(4,146)	$ 692,979
Beginning balance, shares at Dec. 31, 2017	29,639					29,639,374
Net income		20,673				$ 20,673
Cash dividends declared		(2,966)				(2,966)
Payment of deferred fees			(7)	7
Stock option exercises	$ 108					108
Stock option exercises, shares	8
Stock-based compensation	$ 403					403
Stock-based compensation, shares	14
Other comprehensive income (loss)					(5,547)	(5,547)
Ending balance at Mar. 31, 2018	$ 433,305	$ 282,038	$ (3,588)	$ 3,588	$ (9,693)	$ 705,650
Ending balance, shares at Mar. 31, 2018	29,661					29,660,967