Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total		Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2016	$ 201,380		$ 8,578	$ 75,076	$ 119,600	$ (1,874)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13,129				13,129
Other comprehensive income (loss)	1,038					1,038
Stock options exercised	114		5	109
Vesting of restricted stock			7	(7)
Equity based compensation	775		10	765
Cash dividends paid	(6,222)				(6,222)
Ending Balance at Sep. 30, 2017	210,214		8,600	75,943	126,507	(836)
Beginning Balance at Jun. 30, 2017						(1,028)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,787
Other comprehensive income (loss)	192
Ending Balance at Sep. 30, 2017	210,214		8,600	75,943	126,507	(836)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification for ASU 2016-01 adoption	0				650	(650)
Beginning Balance at Dec. 31, 2017	208,717	[1]	8,604	76,179	127,010	(3,076)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,577				17,577
Other comprehensive income (loss)	(5,426)					(5,426)
Stock options exercised	861		35	826
Vesting of restricted stock			11	(11)
Equity based compensation	859		11	848
Cash dividends paid	(6,522)				(6,522)
Ending Balance at Sep. 30, 2018	216,066		8,661	77,842	138,715	(9,152)
Beginning Balance at Jun. 30, 2018						(7,910)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,785
Other comprehensive income (loss)	(1,242)
Ending Balance at Sep. 30, 2018	$ 216,066		$ 8,661	$ 77,842	$ 138,715	$ (9,152)

[1] Derived from audited consolidated financial statements.