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		18,261			18,261
Other Comprehensive Income (Loss)		(2,959)					(2,959)
Cash Dividends Paid	[1]	(6,982)			(6,982)
Stock Options Exercised, Net		1,692		804				888
Shares Issued Under the Directors' Stock Plan		103		72				31
Shares Issued Under the Employee Stock Purchase Plan		252		167				85
Shares Issued for Dividend Reinvestment Plans		856		580				276
Stock-Based Compensation Expense		178		178
Purchases of Treasury Stock		(1,414)						(1,414)
Stockholders' equity, ending balance at Jun. 30, 2018		259,488	18,481	292,020	40,326	(200)	(11,804)	(79,335)
Stockholders' equity, beginning balance at Mar. 31, 2018		252,734	18,481	290,980	34,093	(200)	(11,285)	(79,335)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		9,730			9,730
Other Comprehensive Income (Loss)		(519)					(519)
Cash Dividends Paid	[1]	(3,497)			(3,497)
Stock Options Exercised, Net		1,082		497				585
Shares Issued Under the Directors' Stock Plan		103		72				31
Shares Issued Under the Employee Stock Purchase Plan		136		91				45
Shares Issued for Dividend Reinvestment Plans		425		291				134
Stock-Based Compensation Expense		89		89
Purchases of Treasury Stock		(795)						(795)
Stockholders' equity, ending balance at Jun. 30, 2018		259,488	18,481	292,020	40,326	(200)	(11,804)	(79,335)
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		17,668			17,668
Other Comprehensive Income (Loss)		4,163					4,163
Cash Dividends Paid		(7,528)			(7,528)
Stock Options Exercised, Net		1,325		638				687
Shares Issued Under the Directors' Stock Plan		130		86				44
Shares Issued Under the Employee Stock Purchase Plan		250		163				87
Shares Issued for Dividend Reinvestment Plans		904		615				289
Stock-Based Compensation Expense		194		194
Purchases of Treasury Stock		(2,041)						(2,041)
Stockholders' equity, ending balance at Jun. 30, 2019		284,649	19,035	316,229	39,397	(100)	(9,647)	(80,265)
Stockholders' equity, beginning balance at Mar. 31, 2019		276,609	19,035	315,262	34,231	(100)	(11,567)	(80,252)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		8,934			8,934
Other Comprehensive Income (Loss)		1,920					1,920
Cash Dividends Paid		(3,768)			(3,768)
Stock Options Exercised, Net		790		389				401
Shares Issued Under the Directors' Stock Plan		130		86				44
Shares Issued Under the Employee Stock Purchase Plan		133		87				46
Shares Issued for Dividend Reinvestment Plans		451		306				145
Stock-Based Compensation Expense		99		99
Purchases of Treasury Stock		(649)						(649)
Stockholders' equity, ending balance at Jun. 30, 2019		$ 284,649	$ 19,035	$ 316,229	$ 39,397	$ (100)	$ (9,647)	$ (80,265)

[1] Cash dividends paid per share have been adjusted for the September 27, 2018 3% stock dividend.