Commitments and Contingencies - Supplemental Balance Sheet Information (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Operating leases
Other assets	$ 14,128
Accrued expenses and other liabilities	1,261
Regulatory liabilities and other	12,851
Total operating lease liabilities	14,112
Finance leases
Utility plant	19,034
Accumulated depreciation and amortization	(9,573)
Net utility plant	9,461
Current maturities of long-term debt, net	639
Long-term debt, net	6,010
Total finance lease liabilities	$ 6,649
Weighted average remaining lease term
Operating leases	160 months
Finance leases	82 months
Weighted average discount rate
Operating leases	3.70%
Finance leases	5.60%