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		18,709				18,709
Cash dividends declared		(3,948)				(3,948)
Equity issued pursuant to acquisition	$ 114,478		(7,688)	7,688		114,478
Equity issued pursuant to acquisition, shares	3,799
Payment of deferred fees			3,431	(3,431)
Stock option exercises	$ 287					287
Stock option exercises, shares	16
Stock-based compensation	$ 849					849
Stock-based compensation, shares	18
Other comprehensive income (loss)					2,175	2,175
Ending balance at Jun. 30, 2017	$ 262,901	240,682	(4,257)	4,257	(2,932)	$ 500,651
Ending balance, shares at Jun. 30, 2017	24,678					24,678,295
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		43,403				$ 43,403
Cash dividends declared		(5,934)				(5,934)
Payment of deferred fees			367	(367)
Stock option exercises	$ 324					324
Stock option exercises, shares	25
Stock withheld for payment of taxes
Stock withheld for payment of taxes, shares	(4)
Stock-based compensation	$ 999					999
Stock-based compensation, shares	43
Other comprehensive income (loss)					(7,049)	(7,049)
Ending balance at Jun. 30, 2018	$ 434,117	$ 301,800	$ (3,214)	$ 3,214	$ (11,195)	$ 724,722
Ending balance, shares at Jun. 30, 2018	29,703					29,702,912