Consolidated Statements of Stockholders' Equity (Unaudited) - 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, 2015	$ 213,971		$ 17,421	$ 250,680	$ 32,139		$ (1,100)	$ (7,972)	$ (77,197)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	19,934				19,934
Other Comprehensive Income	2,530	[1]						2,530
Stock Dividend			522	16,415	(16,937)
Cash Dividends Paid	(9,736)				(9,736)	[2]
Stock Options Exercised, Net	1,775			980					795
Shares Issued Under the Directors' Stock Plan	112			76					36
Shares Issued Under the Employee Stock Purchase Plan	358			229					129
Shares Issued for Dividend Reinvestment Plans	1,302			862					440
Stock-Based Compensation Expense	215			215
Tax Benefit for Disposition of Stock Options	63			63
Purchases of Treasury Stock	(1,826)								(1,826)
Allocation of ESOP Stock	510			160			350
Stockholders' Equity, Ending Balance at Sep. 30, 2016	229,208		17,943	269,680	25,400		(750)	(5,442)	(77,623)
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	21,255				21,255
Other Comprehensive Income	699	[1]						699
Stock Dividend			538	16,661	(17,199)
Cash Dividends Paid	(10,119)				(10,119)
Stock Options Exercised, Net	734			335					399
Shares Issued Under the Directors' Stock Plan	126			84					42
Shares Issued Under the Employee Stock Purchase Plan	351			230					121
Shares Issued for Dividend Reinvestment Plans	1,256			843					413
Stock-Based Compensation Expense	261			261
Purchases of Treasury Stock	(2,767)								(2,767)
Stockholders' Equity, Ending Balance at Sep. 30, 2017	$ 244,648		$ 18,481	$ 289,294	$ 22,581		$ (400)	$ (6,135)	$ (79,173)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost.

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