Leases - Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Leased Assets [Line Items]
Operating lease cost	$ 74,728	$ 56,317	$ 113,481	$ 82,842
Variable lease cost	37,810	40,890	100,347	102,782
Short-term lease cost	902	1,038	3,151	2,824
Total lease cost	113,440	98,245	216,979	188,448
Purchased Power Lease Contracts
Operating Leased Assets [Line Items]
Operating lease cost	70,102	51,662	99,616	68,883
Variable lease cost	37,586	40,658	99,613	102,052
Short-term lease cost	0	0	0	0
Total lease cost	107,688	92,320	199,229	170,935
Land, Property & Equipment Leases
Operating Leased Assets [Line Items]
Operating lease cost	4,626	4,655	13,865	13,959
Variable lease cost	224	232	734	730
Short-term lease cost	902	1,038	3,151	2,824
Total lease cost	$ 5,752	$ 5,925	$ 17,750	$ 17,513