Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	0 Months Ended			0 Months Ended
	Mar. 31, 2013	Feb. 15, 2013 Series C	Jan. 15, 2013 Series D	Mar. 04, 2013 Series D	Mar. 22, 2013 Common Shares	Feb. 22, 2013 Common Shares	Apr. 02, 2013 Distribution declared in April 2013 Series C	Apr. 10, 2013 Distribution declared in April 2013 Common Shares
Distributions
Distribution to preferred shareholders (in dollars per share)		$ 0.4375	$ 0.4453
Distribution declared per share (in dollars per share)				$ 0.4453			$ 0.4375	$ 0.47
Distribution to common shareholders (in dollars per share)						$ 0.47
Common Share Issuances
Common stock, shares issued (in shares)					16,100,000
Common stock, issue price (in dollars per share)					$ 25.55
Net proceeds from sale of common shares	$ 393,473				$ 393,473