Cash flow information (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Interest, net*	$ 47,769,000	$ 45,702,000
Income taxes paid, net**	735,000	4,124,000
AFUDC borrowed	1,300,000	1,200,000
Right-of-use assets obtained in exchange for new operating lease liabilities	24,181,000	24,990,000	$ 54,880,000
Property, plant and equipment additions in accounts payable	36,493,000	27,312,000	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, net**	$ 882,000	$ 2,000,000.0