Consolidated Statements of Changes In Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Unallocated ESOP Shares	Accumulated Other Comprehensive Loss	Treasury Stock
Stockholders' equity, beginning balance at Dec. 31, 2017		$ 249,603	$ 18,481	$ 290,219	$ 28,818	$ (200)	$ (8,514)	$ (79,201)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		27,521			27,521
Other Comprehensive Income (Loss)		(3,776)					(3,776)
Stock dividend		0	554	21,126	(21,680)
Cash Dividends Paid	[1]	(10,630)			(10,630)
Stock Options Exercised, Net		1,977		942				1,035
Shares Issued Under the Directors' Stock Plan		103		72				31
Shares Issued Under the Employee Stock Purchase Plan		368		247				121
Shares Issued for Dividend Reinvestment Plans		1,302		890				412
Stock-Based Compensation Expense		267		267
Purchases of Treasury Stock		(1,823)						(1,823)
Stockholders' equity, ending balance at Sep. 30, 2018		264,810	19,035	313,763	24,258	(200)	(12,621)	(79,425)
Stockholders' equity, beginning balance at Jun. 30, 2018		259,488	18,481	292,020	40,326	(200)	(11,804)	(79,335)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		9,260			9,260
Other Comprehensive Income (Loss)		(817)					(817)
Stock dividend		0	554	21,126	(21,680)
Cash Dividends Paid	[1]	(3,648)			(3,648)
Stock Options Exercised, Net		285		138				147
Shares Issued Under the Employee Stock Purchase Plan		116		80				36
Shares Issued for Dividend Reinvestment Plans		446		310				136
Stock-Based Compensation Expense		89		89
Purchases of Treasury Stock		(409)						(409)
Stockholders' equity, ending balance at Sep. 30, 2018		264,810	19,035	313,763	24,258	(200)	(12,621)	(79,425)
Stockholders' equity, beginning balance at Dec. 31, 2018		269,584	19,035	314,533	29,257	(100)	(13,810)	(79,331)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		27,735			27,735
Other Comprehensive Income (Loss)		4,831					4,831
Stock dividend		0	571	17,737	(18,308)
Cash Dividends Paid		(11,309)			(11,309)
Stock Options Exercised, Net		1,640		802				838
Shares Issued Under the Directors' Stock Plan		130		86				44
Shares Issued Under the Employee Stock Purchase Plan		360		236				124
Shares Issued for Dividend Reinvestment Plans		1,333		911				422
Stock-Based Compensation Expense		292		292
Purchases of Treasury Stock		(2,368)						(2,368)
Stockholders' equity, ending balance at Sep. 30, 2019		292,228	19,606	334,597	27,375	(100)	(8,979)	(80,271)
Stockholders' equity, beginning balance at Jun. 30, 2019		284,649	19,035	316,229	39,397	(100)	(9,647)	(80,265)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		10,067			10,067
Other Comprehensive Income (Loss)		668					668
Stock dividend		0	571	17,737	(18,308)
Cash Dividends Paid		(3,781)			(3,781)
Stock Options Exercised, Net		315		164				151
Shares Issued Under the Employee Stock Purchase Plan		110		73				37
Shares Issued for Dividend Reinvestment Plans		429		296				133
Stock-Based Compensation Expense		98		98
Purchases of Treasury Stock		(327)						(327)
Stockholders' equity, ending balance at Sep. 30, 2019		$ 292,228	$ 19,606	$ 334,597	$ 27,375	$ (100)	$ (8,979)	$ (80,271)

[1] Cash dividends paid per share have been adjusted for the September 27, 2019 3% stock dividend.