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
Stockholder's Equity Beginning Balance at Dec. 31, 2014		$ 200,926		$ 17,079		$ 239,721	$ 29,458	$ (1,450)	$ (7,166)	$ (76,716)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		24,662					24,662
Other Comprehensive Loss		(806)							(806)
Stock Dividend				342		8,939	(9,281)
Cash Dividends Paid		(12,700)	[1]				(12,700)
Stock Options Exercised		918				489				429
Shares Issued Under the Directors' Stock Plan		227				143				84
Shares Issued Under the Employee Stock Purchase Plan		494				306				188
Shares Issued for Dividend Reinvestment Plans		886				570				316
Stock-Based Compensation Expense		308				308
Tax Benefit for Exercises of Stock Options		59				59
Purchases of Treasury Stock		(1,498)								(1,498)
Allocation of ESOP Stock		495				145		350
Stockholder's Equity Ending Balance at Dec. 31, 2015		213,971		17,421		250,680	32,139	(1,100)	(7,972)	(77,197)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		26,534					26,534
Other Comprehensive Loss		1,138							1,138
Stock Dividend				522		16,415	(16,937)
Cash Dividends Paid	[1]	(13,092)					(13,092)
Stock Options Exercised		2,404				1,265				1,139
Shares Issued Under the Directors' Stock Plan		205				138				67
Shares Issued Under the Employee Stock Purchase Plan		493				318				175
Shares Issued for Dividend Reinvestment Plans		1,743				1,167				576
Stock-Based Compensation Expense		287				287
Tax Benefit for Exercises of Stock Options		188				188
Purchases of Treasury Stock		(2,141)								(2,141)
Allocation of ESOP Stock		1,122				422		700
Stockholder's Equity Ending 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		29,326					29,326
Other Comprehensive Loss		(35)							(35)
Reclassification due to the adoption of ASU No. 2018-02		(1,645)					1,645		(1,645)
Stock Dividend				538	[2]	16,660	(17,198)
Cash Dividends Paid	[1]	(13,599)					(13,599)
Stock Options Exercised		1,190				544				646
Shares Issued Under the Directors' Stock Plan		233				160				73
Shares Issued Under the Employee Stock Purchase Plan		496				331				165
Shares Issued for Dividend Reinvestment Plans		1,684				1,140				544
Stock-Based Compensation Expense		351				351
Tax Benefit for Exercises of Stock Options		168
Purchases of Treasury Stock		(3,248)								(3,248)
Allocation of ESOP Stock		353				153		200
Stockholder's Equity Ending Balance at Dec. 31, 2017		$ 249,603		$ 18,481		$ 290,219	$ 28,818	$ (200)	$ (8,514)	$ (79,201)

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

[2] Included in the shares issued for the 3% stock dividend in 2017 were treasury shares of 133,152 and unallocated ESOP shares of 584.