Stockholders Equity (Details Textual) (USD $)	1 Months Ended	3 Months Ended			3 Months Ended				1 Months Ended	0 Months Ended	3 Months Ended
	Jan. 31, 2013	Mar. 31, 2013	Mar. 31, 2012	Mar. 29, 2013 investment_bank	Mar. 31, 2013 Restricted Stock [Member]	Mar. 31, 2012 Restricted Stock [Member]	Mar. 31, 2013 Employee Stock Purchase Plan [Member]	Mar. 31, 2012 Employee Stock Purchase Plan [Member] General and Administrative Expense [Member]	Apr. 30, 2013 Subsequent Event [Member]	Apr. 30, 2013 Subsequent Event [Member] Dividend Declared [Member]	Mar. 31, 2013 Cumulative Dividends [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock sold	1,599,271								1,423,931
Proceeds from issuance of common stock	$ 39,700,000	$ 40,424,000	$ 281,000						$ 40,700,000
Equity offering program, shares authorized to be sold				9,000,000					7,576,069
Equity offering program, number of investment banks in sales agreements				4
Dividends per share paid to common stockholders (in dollars per share)											$ 0.3
Dividends per share declared to common stockholders (in dollars per share)		$ 0.30	$ 0.30							$ 0.30
Issued restricted common stock to its employees under stock based incentive plan					66,787	103,225
Shares withheld from its officers to pay taxes					6,061	2,342
Option to purchase to common stock							25,000
Discount on market price on the date of grant							85.00%
Discount on market price on the date of exercise							85.00%
Award expiration date							27 months
Share-based compensation expense								$ 300,000