Leases - Balance Sheet Impact (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Right-of-use assets—Finance leases
Right-of-use assets	$ 302,732	$ 302,732
Less: Accumulated provision for depreciation	(280,782)	(278,586)
Total finance lease assets	$ 21,950	$ 24,146
Finance lease, right-of-use asset, statement of financial position	Right-of-use assets—finance leases	Right-of-use assets—finance leases
Lease liabilities—Finance leases
Obligations under finance leases	$ 38,520	$ 43,586
Long-term debt and finance leases due within one year	9,868	9,351
Total finance lease liabilities	$ 48,388	$ 52,937
Finance lease, liability, current, statement of financial position	Long-term debt and finance leases due within one year	Long-term debt and finance leases due within one year
Right-of-use assets—Operating leases
Electric plant in service, net	$ 8,502	$ 6,587
Total operating lease assets	$ 8,502	$ 6,587
Operating lease, right-of-use asset, statement of financial position	In service	In service
Lease liabilities—Operating leases
Capitalization—Other	$ 6,588	$ 5,152
Other current liabilities	1,914	1,529
Total operating lease liabilities	$ 8,502	$ 6,681
Operating lease, liability, noncurrent, statement of financial position	Other	Other
Operating lease, liability, current, statement of financial position	Other current liabilities	Other current liabilities