Leases - Maturity of our operating lease liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
2020	$ 14,698
2021	11,963
2022	8,331
2023	6,326
2024	4,141
Thereafter	38,697
Total lease commitments	84,156
Less imputed interest	19,571
Total lease liabilities	64,585	$ 119,000
Purchased Power Lease Contracts
Lessee, Lease, Description [Line Items]
2020	0
2021	0
2022	0
2023	0
2024	0
Thereafter	0
Total lease commitments	0
Less imputed interest	0
Total lease liabilities	0
Land, Property & Equipment Leases
Lessee, Lease, Description [Line Items]
2020	14,698
2021	11,963
2022	8,331
2023	6,326
2024	4,141
Thereafter	38,697
Total lease commitments	84,156
Less imputed interest	19,571
Total lease liabilities	$ 64,585