Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		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, 2014		$ 300,322	[1]	$ 7,100		$ 156,581		$ 142,317	$ (5,676)	$ 1,258		$ (1,258)
Beginning Balances, shares at Dec. 31, 2014	[1],[2]			14,588,711
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		41,140						41,140
Other comprehensive loss		(164)							(164)
Dividends		(17,222)						(17,222)
Proceeds from issuance of common stock, net of expenses		0
Stock Issued During Period, Shares, New Issues				592,970
Stock Issued During Period, Value, Acquisitions		30,165		$ 289		29,876
Stock Issued During The Period Value Retirement Savings Plan And Dividend Reinvestment Plan		2,235		$ 21		2,214
Stock Issued During The Period Shares Retirement Savings Plan And Dividend Reinvestment Plan				43,275
Share-based compensation	[3],[4]	1,662		$ 22		1,640
Share-based compensation, shares	[3],[4]			45,703
Treasury stock activities	[1]									625		(625)
Ending Balances at Dec. 31, 2015		358,138	[1]	$ 7,432		190,311		166,235	(5,840)	1,883		(1,883)
Ending Balances, shares at Dec. 31, 2015	[1],[2]			15,270,659
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated other comprehensive loss		(5,840)
Net Income		44,675						44,675
Other comprehensive loss		962							962
Dividends		(18,848)						(18,848)
Proceeds from issuance of common stock, net of expenses	[5]	$ 57,360		$ 467		56,893
Stock Issued During Period, Shares, New Issues		960,488		960,488	[5]
Stock Issued During The Period Value Retirement Savings Plan And Dividend Reinvestment Plan		$ 2,242		$ 17		2,225
Stock Issued During The Period Shares Retirement Savings Plan And Dividend Reinvestment Plan				36,253
Share-based compensation	[3],[4]	1,557		$ 19		1,538
Share-based compensation, shares	[3],[4]			36,099
Treasury stock activities		0								533	[1]	(533)	[1]
Ending Balances at Dec. 31, 2016		446,086	[1]	$ 7,935		250,967		192,062	(4,878)	2,416		(2,416)
Ending Balances, shares at Dec. 31, 2016	[1],[2]			16,303,499
Retained earnings		192,062
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated other comprehensive loss		(4,878)
Net Income		58,124						58,124
Other comprehensive loss		606							606
Dividends		(21,045)						(21,045)
Stock Issued During Period, Shares, Dividend Reinvestment Plan				10,771
Stock Issued During Period, Value, Dividend Reinvestment Plan		735		$ 5		730
Proceeds from issuance of common stock, net of expenses		(10)	[5]	$ 0		(10)	[5]
Stock Issued During Period, Shares, New Issues				0
Share-based compensation	[3],[4]	1,798		$ 15		1,783
Share-based compensation, shares	[3],[4]			30,172
Treasury stock activities	[1]									979		(979)
Ending Balances at Dec. 31, 2017		486,294	[1]	$ 7,955		$ 253,470				$ 3,395		$ (3,395)
Ending Balances, shares at Dec. 31, 2017	[1],[2]			16,344,442
Retained earnings		229,141						$ 229,141
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accumulated other comprehensive loss		$ (4,272)							$ (4,272)

[1] Includes 90,961, 76,745 and 70,631 shares at December 31, 2017, 2016 and 2015, respectively, held in a Rabbi Trust related to our Non-Qualified Deferred Compensation Plan

[2] 2,000,000 shares of preferred stock at $0.01 par value per share have been authorized. No shares have been issued or are outstanding; accordingly, no information has been included in the Statements of Stockholders’ Equity.

[3] Includes amounts for shares issued for directors’ compensation.

[4] The shares issued under the SICP are net of shares withheld for employee taxes. For 2017, 2016 and 2015, we withheld 10,269, 12,031 and 12,620 shares, respectively, for taxes.

[5] On September 22, 2016, we completed a public offering of 960,488 shares of our common stock at a price per share of $62.26. The net proceeds from the sale of common stock, after deducting underwriting commissions and expenses, were approximately $57.4 million.