Quarterly Financial Data - Summary of Quarterly Result of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Revenues from rental properties	$ 23,493	$ 22,324	$ 25,434	$ 28,035	$ 27,593	$ 24,724	$ 24,502	$ 23,444	$ 99,286	$ 100,263	$ 78,227
Earnings from continuing operations	4,362	1,782	2,357	5,307	(16,458)	2,635	13,016	10,231	13,808	9,424	40,867
Net earnings	$ 5,801	$ (3,465)	$ 3,626	$ 6,485	$ (19,482)	$ 5,350	$ 15,202	$ 11,386	$ 12,447	$ 12,456	$ 51,700
Diluted earnings (loss) per common share:
Earnings (loss) from continuing operations	$ 0.13	$ 0.05	$ 0.07	$ 0.16	$ (0.49)	$ 0.08	$ 0.39	$ 0.31	$ 0.41	$ 0.28
Net earnings	$ 0.17	$ (0.10)	$ 0.11	$ 0.19	$ (0.58)	$ 0.16	$ 0.45	$ 0.35	$ 0.37	$ 0.37