Consolidated Statements of Stockholders' Equity (USD $)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Deferred Compensation [Member]	Treasury Stock [Member]
Beginning Balances at Dec. 31, 2011	$ 240,780,000	$ 4,656,000	$ 149,403,000	$ 91,248,000	$ (4,527,000)	$ 817,000	$ (817,000)
Beginning Balances, shares at Dec. 31, 2011		14,350,959
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	28,863,000			28,863,000
Other comprehensive loss	(535,000)				(535,000)
Stock Issued During Period, Value, Dividend Reinvestment Plan				(13,872,000)
Dividends ShareBased Compensation Dividends And Dividends For Reinvestment Plan	(13,879,000)	0	(7,000)			0
Conversion of Debentures	186,000	5,000	181,000
Conversion of debentures, shares		16,463
Share-based compensation	1,183,000	10,000	1,173,000
Share-based compensation, shares		28,826
Treasury stock activities	0	0				165,000	(165,000)
Ending Balances at Dec. 31, 2012	256,598,000	4,671,000	150,750,000	106,239,000	(5,062,000)	982,000	(982,000)
Ending Balances, shares at Dec. 31, 2012		14,396,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	32,787,000			32,787,000
Other comprehensive loss	2,529,000				2,529,000
Stock Issued During Period, Value, Dividend Reinvestment Plan				(14,752,000)
Dividends ShareBased Compensation Dividends And Dividends For Reinvestment Plan	(14,758,000)		(6,000)
Conversion of Debentures	295,000	8,000	287,000
Conversion of debentures, shares		26,075
Share-based compensation	1,322,000	12,000	1,310,000
Share-based compensation, shares		35,022
Treasury stock activities	0					142,000	(142,000)
Ending Balances at Dec. 31, 2013	278,773,000	4,691,000	152,341,000	124,274,000	(2,533,000)	1,124,000	(1,124,000)
Ending Balances, shares at Dec. 31, 2013		14,457,345
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	36,092,000			36,092,000
Other comprehensive loss	(3,143,000)				(3,143,000)
Stock Issued During Period, Value, Dividend Reinvestment Plan				(15,675,000)
Dividends ShareBased Compensation Dividends And Dividends For Reinvestment Plan	(15,675,000)
Stock Issued During The Period Shares Retirement Savings Plan And Dividend Reinvestment Plan		43,367
Stock Issued During The Period Value Retirement Savings Plan And Dividend Reinvestment Plan	1,860,000	16,000	1,844,000
Conversion of Debentures	535,000	15,000	520,000
Conversion of debentures, shares		47,313
Share-based compensation	1,889,000	13,000	1,876,000
Share-based compensation, shares		40,686
Stock Split in Form of Stock Dividend Adjustment to Retained Earnings	(9,000)	2,365,000		(2,374,000)
Treasury stock activities	0					134,000	(134,000)
Ending Balances at Dec. 31, 2014	$ 300,322,000	$ 7,100,000	$ 156,581,000	$ 142,317,000	$ (5,676,000)	$ 1,258,000	$ (1,258,000)
Ending Balances, shares at Dec. 31, 2014		14,588,711