Common and Preferred Shares Common Shares (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended				12 Months Ended								2 Months Ended		12 Months Ended
	Oct. 24, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 23, 2013	Dec. 31, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Dec. 31, 2013 Total Cash Distribution Per Share [Member] Common Stock [Member]	Dec. 31, 2012 Total Cash Distribution Per Share [Member] Common Stock [Member]	Dec. 31, 2013 Taxable Ordinary Income [Member] Common Stock [Member]	Dec. 31, 2012 Taxable Ordinary Income [Member] Common Stock [Member]	Dec. 31, 2013 Return of Capital [Member] Common Stock [Member]	Dec. 31, 2012 Return of Capital [Member] Common Stock [Member]	Feb. 25, 2014 Subsequent Event [Member]	Feb. 26, 2014 Subsequent Event [Member]	Dec. 31, 2013 direct share purchase plan [Member]
Cash Dividends Paid [Line Items]
Common Stock, Shares, Issued		53,361,261	48,454,181		3,600,000										1,280,000	937,652
Common Stock, Dividends, Per Share, Cash Paid								$ 3.6464	$ 2.9500	$ 2.5994	$ 1.8277	$ 1.0470	$ 1.1223
Common stock declared dividends per share						$ 3.16	$ 3.00
Net proceeds from issuance of common shares	$ 174,000	$ 220,785	$ 231	$ 253										$ 46,500		$ 46,300