Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Unallocated ESOP Shares	Accumulated Other Comprehensive Income (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		6,631			6,631
Other Comprehensive Income (Loss)		154					154	[1]
Cash Dividends Paid	[2]	(3,374)			(3,374)
Stock Options Exercised, Net		388		187					201
Shares Issued Under the Directors' Stock Plan		22		14					8
Shares Issued Under the Employee Stock Purchase Plan		106		69					37
Shares Issued for Dividend Reinvestment Plans		425		284					141
Stock-Based Compensation Expense		83		83
Purchases of Treasury Stock		(1,176)							(1,176)
Stockholders' Equity, Ending Balance at Mar. 31, 2017		236,111	17,943	271,517	31,901	(400)	(6,680)		(78,170)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of Change in Accounting Policy	[1]						(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		8,531			8,531
Other Comprehensive Income (Loss)		(2,440)					(2,440)	[1]
Cash Dividends Paid		(3,485)			(3,485)
Stock Options Exercised, Net		610		307					303
Shares Issued Under the Employee Stock Purchase Plan		116		76					40
Shares Issued for Dividend Reinvestment Plans		431		289					142
Stock-Based Compensation Expense		89		89
Purchases of Treasury Stock		(619)							(619)
Stockholders' Equity, Ending Balance at Mar. 31, 2018		$ 252,734	$ 18,481	$ 290,980	$ 34,093	$ (200)	$ (11,285)		$ (79,335)

[1] All amounts are net of tax. Amounts in parentheses indicate debits.

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