Consolidated Statements of Changes In Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Unallocated ESOP Shares	Accumu-lated Other Com- prehensive Loss	Treasury Stock
Stockholders' Equity, Beginning Balance at Dec. 31, 2016		$ 232,852	$ 17,943	$ 270,880	$ 28,644	$ (400)	$ (6,834)	$ (77,381)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		13,839			13,839
Other Comprehensive Income (Loss)		634					634
Cash Dividends Paid	[1]	(6,744)			(6,744)
Stock Options Exercised, Net		701		322				379
Shares Issued Under the Directors' Stock Plan		127		84				43
Shares Issued Under the Employee Stock Purchase Plan		242		160				82
Shares Issued for Dividend Reinvestment Plans		845		569				276
Stock-Based Compensation Expense		172		172
Purchases of Treasury Stock		(1,916)						(1,916)
Stockholders' Equity, Ending Balance at Jun. 30, 2017		240,752	17,943	272,187	35,739	(400)	(6,200)	(78,517)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of change in accounting policy		0					(331)
Impact of change in accounting policy | Accounting Standards Update 2014-09		(102)			(102)
Impact of change in accounting policy | Accounting Standards Update 2016-01					331		(331)
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		(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)

[1] Cash dividends paid per share have been adjusted for the September 28, 2017 3% stock dividend.