Areas of Operation (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Areas of Operation
Operating revenues	$ 33,557,000	$ 36,976,000	$ 24,076,000	$ 51,164,000	$ 27,670,000	$ 40,448,000	$ 36,158,000	$ 49,880,000	$ 145,773,000	$ 154,156,000	$ 156,532,000
Property and equipment	53,549,000				71,541,000				53,549,000	71,541,000
Right-of-use assets	6,605,000								6,605,000
United States
Areas of Operation
Operating revenues									129,452,000	137,101,000	134,442,000
Property and equipment	45,653,000				62,033,000				45,653,000	62,033,000
Right-of-use assets	5,893,000								5,893,000
Canada
Areas of Operation
Operating revenues									16,321,000	17,055,000	$ 22,090,000
Property and equipment	7,896,000				$ 9,508,000				7,896,000	$ 9,508,000
Right-of-use assets	$ 712,000								$ 712,000