Consolidated Statement of Changes in Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Limited Voting Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Noncontrolling Interests
Balance at Dec. 31, 2014	$ 1,679,316	$ 111	$ 4	$ 1,842,581	$ (6,166)	$ (443,757)	$ 286,543
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	7,614					7,275	339
Other comprehensive loss	(3,223)				(3,053)		(170)
Common dividends declared – $0.1875 per share	(21,834)					(20,857)	(977)
Share-based compensation	1,453			1,453
Offering costs associated with the issuance of common stock	(209)			(209)
Issuance of 367,257 shares of common stock upon redemption of Operating Partnership units		1		6,336			(6,337)
Contribution of capital by noncontrolling interests	2,125						2,125
Distributions to noncontrolling interests	(5,894)						(5,894)
Balance at Mar. 31, 2015	$ 1,659,348	$ 112	$ 4	$ 1,850,161	$ (9,219)	$ (457,339)	$ 275,629