Accounting For Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense

	2019		2018		2017
Current income tax expense	$	16,276	$	17,490	$	13,101
Deferred income tax expense	15,098		8,570		69,657
Total income tax expense	$	31,374	$	26,060	$	82,758

Schedule of Effective Income Tax Rate Reconciliation

	2019					2018					2017
Federal income taxes at statutory rates	$	47,909		21.0	%	$	34,158		21.0	%	$	69,542		35.0	%
Increase (decrease) in tax resulting from:
Tax effect of regulatory treatment of utility plant differences	(9,967		)	(4.3	)	(8,153		)	(5.0	)	3,482			1.7
State income tax expense	1,465			0.6		1,191			0.7		1,110			0.6
Settlement of prior year tax returns and adjustment of tax reserves	643			0.3		(140		)	(0.1	)	(384		)	(0.2	)
Manufacturing deduction	—			—		—			—		(1,119		)	(0.6	)
Settlement of equity awards	612			0.3		(990		)	(0.6	)	(1,439		)	(0.7	)
Acquisition costs	(1,712		)	(0.7	)	329			0.2		2,491			1.3
Federal income tax rate change	—			—		—			—		10,169			5.1
Non-plant excess deferred turnaround	(5,690		)	(2.5	)	—			—		—			—
Tax loss on sale of METALfx	(1,272		)	(0.6	)	—			—		—			—
Valuation allowance	267			0.1		—			—		—			—
Other	(881		)	(0.4	)	(335		)	(0.2	)	(1,094		)	(0.5	)
Total income tax expense	$	31,374		13.8	%	$	26,060		16.0	%	$	82,758		41.7	%

Schedule of Deferred Income Tax Assets and Liabilities

The total net deferred income tax liability consisted of the following as of December 31 (dollars in thousands):

	2019			2018
Deferred income tax assets:
Unfunded benefit obligation	$	43,224		$	45,842
Utility energy commodity and interest rate swap derivatives	8,436			11,724
Regulatory deferred tax credits	6,394			6,244
Tax credits	21,696			21,008
Power and natural gas deferrals	8,624			17,618
Deferred compensation	7,171			5,536
Deferred taxes on regulatory liabilities	101,648			106,909
Other	17,423			16,793
Total gross deferred income tax assets	214,616			231,674
Valuation allowances for deferred tax assets	(16,550		)	(13,651		)
Total deferred income tax assets after valuation allowances	198,066			218,023
Deferred income tax liabilities:
Differences between book and tax basis of utility plant	525,931			509,789
Regulatory asset on utility, property plant and equipment	86,701			83,141
Regulatory asset for pensions and other postretirement benefits	43,838			47,893
Utility energy commodity and interest rate swap derivatives	8,436			11,724
Long-term debt and borrowing costs	26,552			24,609
Settlement with Coeur d’Alene Tribe	6,250			6,400
Other regulatory assets	20,137			15,318
Other	8,734			6,751
Total deferred income tax liabilities	726,579			705,625
Net long-term deferred income tax liability	$	528,513		$	487,602