Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 9,497	$ 9,669	$ 6,115	$ 13,600	$ 13,051	$ 15,908	$ 18,246	$ 21,258	$ 38,881	$ 68,463	$ 97,199
Operating income (loss)	1,469	2,014	(1,104)	5,602	4,968	8,081	10,776	13,331	7,981	37,156	63,182
Net income (loss) attributable to common shareholders	$ (1,375)	$ 1,560	$ (368)	$ 7,883	$ 1,118	$ 16,400	$ 2,406	$ 495	$ 7,700	$ 20,419	$ 117,925
Net income (loss) per share:
Common shares - basic	$ (0.03)	$ 0.03	$ (0.01)	$ 0.17	$ 0.02	$ 0.36	$ 0.05	$ 0.01	$ 0.17	$ 0.44	$ 0.81
Common shares - diluted	$ (0.03)	$ 0.02	$ (0.01)	$ 0.11	$ 0.02	$ 0.22	$ 0.05	$ 0.01	$ 0.11	$ 0.39	$ 0.53
Weighted average number of shares outstanding:
Common shares - basic	46,099	46,055	46,001	45,967	45,956	45,899	45,858	45,856	46,031	45,893	45,855
Common shares - diluted	46,099	86,055	46,001	85,967	45,956	85,899	45,858	45,856	86,031	85,893	85,855