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, 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		0		522		16,415	(16,937)
Cash Dividends Paid		(13,092)	[1]				(13,092)
Shares Issued for Stock Option Exercises, net		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 Benefits Related to Stock Options Exercised		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)
Stock Dividend		0		538		16,660	(17,198)
Cash Dividends Paid	[1]	(13,599)					(13,599)
Shares Issued for Stock Option Exercises, net		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 Benefits Related to Stock Options Exercised		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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of ASU adoption | Accounting Standards Update 2014-09		(102)					(102)
Impact of ASU adoption | Accounting Standards Update 2016-01		$ 0					331		(331)
Treasury shares (in shares)		4,541,524
Unallocated ESOP shares (in shares)		9,643
Net Income		$ 36,279					36,279
Other Comprehensive Loss		(4,965)							(4,965)
Stock Dividend		0		554	[2]	21,126	(21,680)
Cash Dividends Paid	[1]	(14,389)					(14,389)
Shares Issued for Stock Option Exercises, net		2,255				1,079				1,176
Shares Issued Under the Directors' Stock Plan		205				142				63
Shares Issued Under the Employee Stock Purchase Plan		505				340				165
Shares Issued for Dividend Reinvestment Plans		1,761				1,197				564
Stock-Based Compensation Expense		356				356
Tax Benefits Related to Stock Options Exercised		240
Purchases of Treasury Stock		(2,098)								(2,098)
Allocation of ESOP Stock		174				74		100
Stockholder's Equity Ending 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]
Treasury shares (in shares)		4,558,207
Unallocated ESOP shares (in shares)		5,001

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

[2] Included in the shares issued for the 3% stock dividend in 2018 were treasury shares of 133,358 and unallocated ESOP shares of 289.