Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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]
Total revenues	$ 28,243	$ 27,106	$ 25,701	$ 23,629	$ 22,632	$ 17,985	$ 17,376	$ 16,958	$ 104,679	$ 74,951	$ 58,897
Net income (loss)	$ 8,388	$ 7,832	$ 7,631	$ 5,502	$ 5,003	$ 727	$ 2,266	$ 2,038	$ 29,353	$ 10,034	$ (8,143)
Earnings (loss) per common share, basic (in usd per share)	$ 0.14	$ 0.13	$ 0.13	$ 0.11	$ 0.10	$ 0.02	$ 0.07	$ 0.06	$ 0.52	$ 0.26	$ (0.36)
Earnings (loss) per common share, diluted (in usd per share)	$ 0.14	$ 0.13	$ 0.13	$ 0.11	$ 0.10	$ 0.02	$ 0.07	$ 0.06	$ 0.52	$ 0.26	$ (0.36)
Weighted-average number of common shares outstanding, basic (in shares)	60,875	57,595	57,478	48,101	47,660	39,125	31,278	31,257	56,030	37,380	22,788
Weighted-average number of common shares outstanding, diluted (in shares)	60,875	57,595	57,478	48,101	47,660	39,125	31,278	31,257	56,030	37,380	22,788