Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Net increase (decrease) in shareholders' equity resulting from operations
Net Income (Loss) Attributable to Parent	$ 20,947		$ 11,600		$ 43,582		$ 51,935
Net Income (Loss) Attributable to Participating Non-controlling Interest	172	[1]	105	[1]	357	[1]	516	[1]
Net income (loss) attributable to parent and participating non-controlling interest	21,119		11,705		43,939		52,451
Net increase in shareholders' equity resulting from operations– common shares	20,614		11,404		42,889		51,003
Net increase in shareholders' equity resulting from operations– LTIP units	333		196		693		932
Dividends Paid(2):
Common shareholders	(19,590)	[2]	(19,567)	[2]	(39,180)	[2]	(50,581)	[2]
LTIP unit holders	(317)	[2]	(306)	[2]	(633)	[2]	(910)	[2]
Non-controlling Interest	(163)	[2]	(163)	[2]	(327)	[2]	(485)	[2]
Total dividends paid to common shareholders, LTIP unit holders, and non-controlling interest	(20,070)	[2]	(20,036)	[2]	(40,140)	[2],[3]	(51,976)	[2],[3]
Undistributed (Distributed in excess of) earnings:
Common shareholders	1,024		(8,163)		3,709		422
LTIP Unit holders	16		(110)		60		22
Non-controlling interest	9		(58)		30		31
Total undistributed (distributed in excess of) earnings attributable to common shareholders, LTIP unit holders, and non-controlling interest	1,049		(8,331)		3,799		475
Weighted average shares outstanding (basic and diluted):
Weighted average common shares outstanding	25,441,750		23,046,550		25,438,677		21,724,721
Weighted average participating LTIP units	411,052		397,096		411,052		397,096
Weighted average non-controlling interest units	212,000		212,000		212,000		212,000
Basic earnings per common share:
Distributed (in usd per share)	$ 0.77		$ 0.77		$ 1.54		$ 2.29
Undistributed (in usd per share)	$ 0.04		$ (0.28)		$ 0.15		$ 0.06
Basic earnings per common share (in usd per share)	$ 0.81		$ 0.49		$ 1.69		$ 2.35
Diluted earnings per common share:
Distributed (in usd per share)	$ 0.77		$ 0.77		$ 1.54		$ 2.29
Undistributed (in usd per share)	$ 0.04		$ (0.28)		$ 0.15		$ 0.06
Diluted earnings per common share (in usd per share)	$ 0.81		$ 0.49		$ 1.69		$ 2.35
Net Income (Loss) Attributable to Non-Participating Non-controlling Interest	$ 85				$ 103

[1] For the three and six month periods ended June 30, 2014, excludes net increase in equity resulting from operations of $85.0 thousand and $103.0 thousand, respectively attributable to the joint venture partner, which has a non-participating interest as described in Note 9.

[2] The Company pays quarterly dividends in arrears, so a portion of the dividends paid in each calendar year relate to the prior year's earnings.

[3] For the six month periods ended June 30, 2014 and 2013, dividends totaling $1.54 and $2.29, respectively, per common share and convertible unit outstanding, were declared and paid.