Shareholders' Equity (Details 2) (USD $)	0 Months Ended				3 Months Ended								12 Months Ended
	Nov. 22, 2013	Aug. 22, 2013	May 24, 2013	Feb. 22, 2013	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 03, 2014
Distributions
Cash distribution to common shareholders (in dollars per share)	$ 0.43	$ 0.43	$ 0.43	$ 0.43
Distribution payable to common shareholders (in dollars per share)																$ 0.43
Cash distribution per common share paid or accrued (in dollars per share)					$ 0.43	$ 0.43	$ 0.43	$ 0.43	$ 0.43	$ 0.42	$ 0.42	$ 0.42	$ 1.72	$ 1.69	$ 1.67
Characterization of distributions paid or accrued as a percentage of ordinary income													82.92%	80.36%	92.88%
Characterization of distributions paid or accrued as a percentage of return of capital													9.55%	19.64%	7.12%
Characterization of distributions paid or accrued as a percentage of capital gain													7.01%
Characterization of distributions paid or accrued as a percentage of Internal Revenue Code section 1250 gain													0.52%