Quarterly Information (unaudited) - Schedule of Quarterly Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenues from continuing operations	$ 34,777	$ 33,303	$ 30,608	$ 27,504	$ 26,164	$ 23,674	$ 22,722	$ 21,340	$ 126,192	$ 93,900	$ 66,581
Net operating income	25,310	23,966	22,538	19,827	18,941	17,098	16,407	15,160
Net income (loss) from continuing operations									25,876	1,950	(1,170)
Income (loss) from discontinued operations									0	0	2,146
Net income (loss)	8,546	3,061	12,792	1,477	1,056	617	196	81	25,876	1,950	976
Net income (loss) attributable to common stockholders	$ 6,928	$ 2,267	$ 12,299	$ 1,347	$ 945	$ 540	$ 139	$ 27	$ 25,126	$ 1,874	$ 896
Net income attributable to common stockholders per share - basic (in dollars per share)	$ 0.11	$ 0.03	$ 0.19	$ 0.02
Net income attributable to common stockholders per share - diluted (in dollars per share)	$ 0.10	$ 0.03	$ 0.19	$ 0.02
Net income (loss) available to common stockholders per share - basic and diluted (in dollars per share)					$ 0.02	$ 0.01	$ 0.00	$ 0.00	$ 0.36	$ 0.03	$ 0.02