Income Taxes (Tables)

6 Months Ended

Jun. 30, 2021

Income Tax Disclosure [Abstract]

Summary of Significant Factors Impact on Difference Between Effective Tax Rate and Federal Statutory Rate

The following table summarizes the significant factors impacting the difference between our effective tax rate and the federal statutory rate for the three and six months ended June 30 (dollars in thousands):

	Three months ended June 30,										Six months ended June 30,
	2021					2020					2021					2020
Federal income taxes at statutory rates	$	3,459		21.0	%	$	2,002		21.0	%	$	20,297		21.0	%	$	13,963		21.0	%
Increase (decrease) in tax resulting from:
Tax effect of regulatory treatment of utility       plant differences		(3,204	)	(19.5	)		(2,415	)	(25.3	)		(6,444	)	(6.7	)		(4,817	)	(7.2	)
State income tax expense		280		1.7			(325	)	(3.4	)		832		0.9			902		1.4
Non-plant excess deferred turnaround (1)		—		—			(8,390	)	(88.0	)		—		—			(8,476	)	(12.7	)
Settlement of equity awards		(21	)	(0.1	)		—		—			909		1.0			165		0.1
Other		1,884		11.5			1,209		12.7			(1,032	)	(1.1	)		(1,124	)	(1.7	)
Total income tax expense	$	2,398		14.6	%	$	(7,919	)	(83.0	)%	$	14,562		15.1	%	$	613		0.9	%

(1)In March 2020, the WUTC approved an all-party settlement agreement related to electric tax benefits that were set aside for Colstrip in the 2020 general rate case order. In the approved settlement agreement, the parties agreed to utilize $10.9 million ($8.4 million when tax-effected) of the electric tax benefits to offset costs associated with accelerating the depreciation of Colstrip Units 3 & 4, to reflect a remaining useful life of those units through December 31, 2025. In the second quarter 2020, the Company recorded a one-time increase to depreciation expense with an offsetting decrease to income tax expense.