Leases - Lease costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Operating Leased Assets [Line Items]
Operating lease cost	$ 60,228
Variable lease cost	114,015
Short-term lease cost	4,385
Total lease cost	178,628
Purchased Power Lease Contracts
Operating Leased Assets [Line Items]
Operating lease cost	42,190
Variable lease cost	113,233
Short-term lease cost	0
Total lease cost	155,423
Land, Property & Equipment Leases
Operating Leased Assets [Line Items]
Operating lease cost	18,038
Variable lease cost	782
Short-term lease cost	4,385
Total lease cost	$ 23,205