Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Net increase (decrease) in shareholders' equity resulting from operations
Net Income (Loss) Attributable to Parent	$ 12,948		$ 11,727		$ 56,530		$ 63,662
Net Income (Loss) Attributable to Participating Non-controlling Interest	98	[1]	96	[1]	456	[1]	612	[1]
Net income (loss) attributable to parent and participating non-controlling interest	13,046		11,823		56,986		64,274
Net increase in shareholders' equity resulting from operations– common shares	12,756		11,546		55,653		62,579
Net increase in shareholders' equity resulting from operations– LTIP units	192		181		877		1,083
Dividends Paid(2):
Common shareholders	(19,590)	[2]	(19,571)	[2]	(58,934)	[2]	(70,152)	[2]
LTIP unit holders	(317)	[2]	(306)	[2]	(950)	[2]	(1,216)	[2]
Non-controlling Interest	(163)	[2]	(163)	[2]	(326)	[2]	(648)	[2]
Total dividends paid to common shareholders, LTIP unit holders, and non-controlling interest	(20,070)	[2]	(20,040)	[2]	(60,210)	[2],[3]	(72,016)	[2],[3]
Undistributed (Distributed in excess of) earnings:
Common shareholders	(6,834)		(8,025)		(3,281)		(7,573)
LTIP Unit holders	(125)		(125)		(73)		(133)
Non-controlling interest	(65)		(67)		130		(36)
Total undistributed (distributed in excess of) earnings attributable to common shareholders, LTIP unit holders, and non-controlling interest	(7,024)		(8,217)		(3,224)		(7,742)
Weighted average shares outstanding (basic and diluted):
Weighted average common shares outstanding	27,442,146		25,415,809		26,113,839		22,968,604
Weighted average participating LTIP units	411,926		397,897		411,346		397,366
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		$ 2.31		$ 3.06
Undistributed (in usd per share)	$ (0.31)		$ (0.32)		$ (0.18)		$ (0.33)
Basic earnings per common share (in usd per share)	$ 0.46		$ 0.45		$ 2.13		$ 2.73
Diluted earnings per common share:
Distributed (in usd per share)	$ 0.77		$ 0.77		$ 2.31		$ 3.06
Undistributed (in usd per share)	$ (0.31)		$ (0.32)		$ (0.18)		$ (0.33)
Diluted earnings per common share (in usd per share)	$ 0.46		$ 0.45		$ 2.13		$ 2.73
Net Income (Loss) Attributable to Non-Participating Non-controlling Interest	$ 100				$ 200

[1] For the three and nine month periods ended September 30, 2014, excludes net increase in equity resulting from operations of $0.1 million and $0.2 million, 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 nine month periods ended September 30, 2014 and 2013, dividends totaling $2.31 and $3.06, respectively, per common share and convertible unit outstanding, were declared and paid.