Cash flow information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Interest, net	$ 15,978,000	$ 19,067,000
Income taxes paid (refunded), net	(1,000)	29,000
AFUDC borrowed	627,000	556,000
Right-of-use assets obtained in exchange for new operating lease liabilities	10,655,000	2,731,000	$ 54,880,000
Property, plant and equipment additions in accounts payable	27,425,000	27,655,000	46,119,000
Accrual for holdback payment related to a business combination	5,000,000	0	0
Debt assumed in connection with a business combination	0	1,163,000	$ 1,163,000
Continuing and discontinued operations
Income taxes paid (refunded), net	$ 146,000	$ 132,000