Accounting For Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense

	2015		2014			2013
Current income tax expense (benefit)	$	12,212	$	(67,059	)	$	37,743
Deferred income tax expense	55,237		139,299			20,271
Total income tax expense	$	67,449	$	72,240		$	58,014

Schedule of Effective Income Tax Rate Reconciliation

	2015					2014					2013
Federal income taxes at statutory rates	$	64,967		35.0	%	$	67,237		35.0	%	$	56,821		35.0	%
Increase (decrease) in tax resulting from:
Tax effect of regulatory treatment of utility plant differences	4,358			2.3		4,008			2.1		3,532			2.2
State income tax expense	1,012			0.5		506			0.2		1,553			1.0
Settlement of prior year tax returns and adjustment of tax reserves	(992		)	(0.5	)	1,104			0.6		(1,104		)	(0.7	)
Manufacturing deduction	(1,198		)	(0.6	)	(169		)	(0.1	)	(2,033		)	(1.3	)
Other	(698		)	(0.4	)	(446		)	(0.2	)	(755		)	(0.5	)
Total income tax expense	$	67,449		36.3	%	$	72,240		37.6	%	$	58,014		35.7	%

Schedule of Deferred Income Tax Assets and Liabilities

	2015			2014
Deferred income tax assets:
Unfunded benefit obligation	$	75,716		$	72,324
Derivatives	47,009			46,903
Tax credits	15,011			15,080
Power and natural gas deferrals	12,866			3,811
Deferred compensation	10,354			10,796
Other	29,471			20,583
Total gross deferred income tax assets	190,427			169,497
Valuation allowances for deferred tax assets	(2,862		)	(8,145		)
Total deferred income tax assets after valuation allowances	187,565			161,352
Deferred income tax liabilities:
Differences between book and tax basis of utility plant	723,661			654,321
Regulatory asset on utility, property plant and equipment	36,917			36,504
Regulatory asset for pensions and other postretirement benefits	82,253			82,515
Utility energy commodity derivatives	47,010			46,906
Long-term debt and borrowing costs	14,027			11,484
Settlement with Coeur d’Alene Tribe	12,084			12,458
Other regulatory assets	11,691			9,691
Other	7,399			3,021
Total deferred income tax liabilities	935,042			856,900
Net deferred income tax liability	$	747,477		$	695,548
Consolidated balance sheet classification of net deferred income taxes:
Current deferred income tax asset (1)	$	—		$	14,794
Long-term deferred income tax liability (1)	747,477			710,342
Net deferred income tax liability	$	747,477		$	695,548

Schedule of Recovery of Deferred Income Tax Liabilities

	2015		2014
Regulatory assets for deferred income taxes	$	101,240	$	100,412
Regulatory liabilities for deferred income taxes	17,609		14,534