Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Tax treatment of distributions:
Ordinary income (in dollars per share)	$ 2.65787	$ 2.23124	$ 2.28131
Qualified ordinary income (in dollars per share)	$ 0.03718	$ 0.00000	$ 0.00000
Long-term capital gain (in dollars per share)	$ 0.03995	$ 0.18884	$ 0.01869
Unrecaptured Section 1250 gain (in dollars per share)	$ 0.00000	$ 0.05992	$ 0.00000
Distribution reported for 1099-DIV purposes (in dollars per share)	$ 2.73500	$ 2.48000	$ 2.30000
REIT distribution requirement (as a percent)	90.00%	90.00%	90.00%
Provision (benefit) for income taxes
Current	$ 2,684,000	$ 1,208,000	$ (4,080,000)
Deferred	(14,512,000)	(7,490,000)	(26,580,000)
Income tax expense (benefit)	(11,828,000)	(6,282,000)	(30,660,000)
Canadian income tax benefit included in consolidated benefit for income taxes	$ (300,000)	$ (700,000)	$ (500,000)