Leases Capital Leases (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) renewal_option	Dec. 31, 2017 USD ($)
Capital Leases [Line Items]
Lessee Leasing Arrangements, Capital Leases, Number of Lease Renewal Periods | renewal_option	2
Capital lease obligations, current portion	$ 0	$ 2,309,000
Lessee Leasing Arrangements, Capital Leases, Term Of Contract	25 years
Capital Leases, Future Minimum Payments Due, Next Twelve Months	$ 2,064,000
Capital Leases, Future Minimum Payments Due in Two Years	2,124,000
Capital Leases, Future Minimum Payments Due in Three Years	2,243,000
Capital Leases, Future Minimum Payments Due in Four Years	2,306,000
Capital Leases, Future Minimum Payments Due in Five Years	2,432,000
Capital Leases, Future Minimum Payments Due Thereafter	28,898,000
Capital Leases, Future Minimum Payments Due	40,067,000
Capital Leases, Future Minimum Payments, Interest Included in Payments	(20,601,000)
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	$ 19,466,000
Lessee Leasing Arrangements, Capital Leases, Renewal Term, Option One	10 years
Lessee Leasing Arrangements, Capital Leases, Renewal Term, Option Two	5 years
Substation equipment
Capital Leases [Line Items]
Capital Leased Assets, Gross	$ 100,000	500,000
Lessee Leasing Arrangements, Capital Leases, Term Of Contract	39 years
Costs Incurred, Development of Property, Plant And Equipment, In Property, Plant And Equipment	$ 100,000	1,000,000
Capital Leases, Future Minimum Payments Due	0
Industrial Development Revenue Bond [Member]
Capital Leases [Line Items]
Capital Leased Assets, Gross	6,100,000
Fiber Facilities [Member]
Capital Leases [Line Items]
Capital Leased Assets, Gross	12,300,000	15,200,000
Capital lease obligations, current portion	$ 300,000	$ 2,300,000
Lessee Leasing Arrangements, Capital Leases, Renewal Term, Option One	25 years