Leases - Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating Leased Assets [Line Items]
Operating lease cost	$ 34,112	$ 21,872	$ 38,753	$ 26,525
Variable lease cost	40,795	41,076	62,537	61,892
Short-term lease cost	1,260	996	2,249	1,786
Total lease cost	76,167	63,944	103,539	90,203
Purchased Power Lease Contracts
Operating Leased Assets [Line Items]
Operating lease cost	29,514	17,221	29,514	17,221
Variable lease cost	40,539	40,821	62,027	61,394
Short-term lease cost	0	0	0	0
Total lease cost	70,053	58,042	91,541	78,615
Land, Property & Equipment Leases
Operating Leased Assets [Line Items]
Operating lease cost	4,598	4,651	9,239	9,304
Variable lease cost	256	255	510	498
Short-term lease cost	1,260	996	2,249	1,786
Total lease cost	$ 6,114	$ 5,902	$ 11,998	$ 11,588