Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Schedule of lease costs

The following table provides information related to our lease costs (dollars in thousands):

	Year Ended December 31, 2020						Year Ended December 31, 2019
	Purchased Power Lease Contracts		Land, Property & Equipment Leases		Total		Purchased Power Lease Contracts		Land, Property & Equipment Leases		Total
Operating lease cost	$	68,883	$	18,493	$	87,376	$	42,190	$	18,038	$	60,228
Variable lease cost	121,359		972		122,331		113,233		782		114,015
Short-term lease cost	—		3,804		3,804		—		4,385		4,385
Total lease cost	$	190,242	$	23,269	$	213,511	$	155,423	$	23,205	$	178,628

The following tables provide other additional information related to operating lease liabilities (dollars in thousands):

	Year Ended December 31, 2020		Year Ended December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities — operating cash flows:	$	75,097	$	69,075
Right-of-use operating lease assets obtained in exchange for operating lease liabilities	441,653		11,262

	December 31, 2020		December 31, 2019
Weighted average remaining lease term	6 years		13 years
Weighted average discount rate (a)	1.69	%	3.71	%

(a)Most of our lease agreements do not contain an implicit rate that is readily determinable. For these agreements we use our incremental borrowing rate to measure the present value of lease liabilities. We determine our incremental borrowing rate at lease commencement based on the rate of interest that we would have to pay to borrow, on a collateralized basis over a similar term, an amount equal to the lease payments in a similar economic environment. We use the implicit rate when it is readily determinable.

Schedule of maturities of operating lease liabilities

The following table provides information related to the maturity of our operating lease liabilities (dollars in thousands):

	December 31, 2020
Year	Purchased Power Lease Contracts		Land, Property & Equipment Leases		Total
2021	$	66,658	$	14,455	$	81,113
2022	68,325		10,849		79,174
2023	70,033		8,503		78,536
2024	71,784		6,104		77,888
2025	73,578		4,400		77,978
Thereafter	36,760		37,314		74,074
Total lease commitments	387,138		81,625		468,763
Less imputed interest	14,375		18,267		32,642
Total lease liabilities	$	372,763	$	63,358	$	436,121