Leases (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Lease cost

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

	Year Ended December 31, 2019
	Purchased Power Lease Contracts		Land, Property & Equipment Leases		Total
Operating lease cost	$	42,190	$	18,038	$	60,228
Variable lease cost	113,233		782		114,015
Short-term lease cost	—		4,385		4,385
Total lease cost	$	155,423	$	23,205	$	178,628

The following tables provide other additional information related to operating lease liabilities:

	December 31, 2019
Weighted average remaining lease term	13 years
Weighted average discount rate (a)	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.

	Year Ended December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities - operating cash flows (dollars in thousands):	$	69,075

Schedule of future minimum payments

The following table provides information related to estimated future minimum operating lease payments (dollars in thousands):

	December 31, 2018
Year	Purchased Power Lease Contracts		Land, Property & Equipment Leases		Total
2019	$	54,499	$	13,747	$	68,246
2020	—		12,428		12,428
2021	—		9,478		9,478
2022	—		6,513		6,513
2023	—		5,359		5,359
Thereafter	—		42,236		42,236
Total future lease commitments	$	54,499	$	89,761	$	144,260

Maturity of our operating lease liabilities

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

	December 31, 2019
Year	Purchased Power Lease Contracts (a)		Land, Property & Equipment Leases		Total
2020	$	—	$	14,698	$	14,698
2021	—		11,963		11,963
2022	—		8,331		8,331
2023	—		6,326		6,326
2024	—		4,141		4,141
Thereafter	—		38,697		38,697
Total lease commitments	—		84,156		84,156
Less imputed interest	—		19,571		19,571
Total lease liabilities	$	—	$	64,585	$	64,585

(a) As of December 31, 2019, we had no operating lease liabilities relating to purchased power lease contracts. See discussion below regarding executed contracts with commencement dates beginning in June 2020.