Quarterly Data - Additional Information (Details) - USD ($) $ / shares in Units, $ 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	$ 97,320	$ 92,999	$ 76,599	$ 76,666	$ 73,674	$ 70,010	$ 53,216	$ 44,134	$ 343,584	$ 241,034	$ 129,441
Operating income	9,523	12,511	4,994	6,688	8,590	10,267	7,158	5,392	33,716	31,407	12,507
Net income	10,187	12,539	10,331	6,716	8,620	10,294	7,184	5,424	39,773	31,522	12,741
Net income attributable to common shareholders	$ 9,536	$ 12,018	$ 9,670	$ 6,191	$ 7,825	$ 9,427	$ 6,486	$ 4,386	$ 37,415	$ 28,124	$ 10,599
Earnings per share – basic:
Earnings per share - basic (in dollars per share)	$ 0.05	$ 0.07	$ 0.06	$ 0.04	$ 0.06	$ 0.07	$ 0.05	$ 0.04	$ 0.23	$ 0.22	$ 0.15
Weighted average number of shares outstanding - basic (in shares)	179,683,948	177,847,424	155,366,080	138,986,629	135,581,976	134,608,396	131,481,329	102,704,008	163,123,109	126,143,114	72,750,724
Earnings per share – diluted:
Earnings per share - diluted (in dollars per share)	$ 0.05	$ 0.07	$ 0.06	$ 0.04	$ 0.06	$ 0.07	$ 0.05	$ 0.04	$ 0.23	$ 0.22	$ 0.15
Weighted Average Number of Shares Outstanding, Diluted	185,273,236	183,298,145	161,012,360	142,605,930	139,602,349	138,880,787	135,944,722	107,148,380	168,231,299	130,466,893	76,792,073