Quarterly Financial Data (Unaudited) - Schedule Of Quarterly Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Data [Abstract]
Operating Revenues	$ 45,257	$ 39,749	$ 31,674	$ 31,447	$ 25,821	$ 28,249	$ 27,910	$ 18,403
Operating Income (Loss)	9,347	6,729	(537)	(12,204)	(2,034)	4,835	3,563	(2,783)	$ 3,335	$ 3,581	$ 11,005
Net income (loss)	$ 5,493	$ 8,896	$ (4,652)	$ (14,265)	$ 2,454	$ (2,084)	$ (1,583)	$ 5,816	$ (4,528)	$ 4,603	$ 5,820