Equity (Details 2) (USD $)	3 Months Ended		12 Months Ended					3 Months Ended			3 Months Ended		1 Months Ended						3 Months Ended		12 Months Ended
	Mar. 31, 2014 item	Mar. 31, 2013	Dec. 31, 2012 item	Dec. 31, 2013	Jun. 30, 2014 Subsequent Event Dividend distributions	May 30, 2014 Subsequent Event Dividend distributions	Apr. 30, 2014 Subsequent Event Dividend distributions	Mar. 31, 2013 Equity Distribution Agreement	Dec. 31, 2013 Equity Distribution Agreement	Jul. 19, 2013 Shelf Registration	Mar. 31, 2014 Series C Cumulative Convertible Preferred Stock	Mar. 31, 2013 Series C Cumulative Convertible Preferred Stock	Mar. 31, 2014 Common Stock	Feb. 28, 2014 Common Stock	Jan. 31, 2014 Common Stock	Mar. 31, 2013 Common Stock	Feb. 28, 2013 Common Stock	Jan. 31, 2013 Common Stock	Mar. 31, 2014 Common Stock	Mar. 31, 2013 Common Stock	Dec. 31, 2013 Common Stock Equity Distribution Agreement
Equity
Shares outstanding	2,000,000			2,000,000							2,000,000
Dividend Rate (as a percent)											8.50%
Number of shares of common stock to be issued upon conversion											2,000,000
Conversion price per share											$ 19.25
Total shares reserved for issuance of common stock related to the conversion of preferred stock											2,000,000
Number of shares repurchased																			200	600
Maximum aggregate offering price of shares authorized for issuance under terminated agreement									$ 85,686,000
Shares common stock sold								126,742
Net proceeds								4,895,000
Reclassification of accumulated costs to additional paid in capital																					662,000
Maximum offering capacity under shelf registration statement										800,000,000
Non-controlling Interests
Number of limited partners	0
Number of limited partnerships			1
Limited partnership, conversion basis			1
Payment of accrued distributions to former limited partners		7,000
Dividend Distributions
Declared	18,560,000	15,035,000									818,000	818,000	17,742,000			14,217,000			17,742,000	14,217,000
Paid	18,560,000	15,035,000									818,000	818,000							17,742,000	14,217,000
Cash dividend declared per common share per month (in dollars per share)													$ 0.17	$ 0.17	$ 0.17	$ 0.155	$ 0.155	$ 0.155
Cash dividend declared per common share per month (in dollars per share)					$ 0.17	$ 0.17	$ 0.17
Cash dividend paid per common share per month (in dollars per share)													$ 0.17	$ 0.17	$ 0.17	$ 0.155	$ 0.155	$ 0.155
Accumulated other comprehensive income
Accumulated other comprehensive income	$ 108,000			$ 117,000