Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 36,597	$ 32,948	$ 32,829	$ 30,608	$ 28,243	$ 27,106	$ 25,701	$ 23,629	$ 132,982	$ 104,679	$ 74,951
Net income	$ 2,252	$ 11,311	$ 2,030	$ 10,281	$ 8,388	$ 7,832	$ 7,631	$ 5,502	$ 25,874	$ 29,353	$ 10,034
Earnings per common share, basic (usd per share)	$ 0.03	$ 0.15	$ 0.03	$ 0.15	$ 0.14	$ 0.13	$ 0.13	$ 0.11	$ 0.35	$ 0.52	$ 0.26
Earnings per common share, diluted (usd per share)	$ 0.03	$ 0.15	$ 0.03	$ 0.15	$ 0.14	$ 0.13	$ 0.13	$ 0.11	$ 0.35	$ 0.52	$ 0.26
Weighted-average number of common shares outstanding, basic (shares)	75,476	75,471	72,564	66,951	60,875	57,595	57,478	48,101	72,647	56,030	37,380
Weighted-average number of common shares outstanding, diluted (shares)	75,476	75,471	72,564	66,951	60,875	57,595	57,478	48,101	72,647	56,030	37,380