Income Taxes (Tables)

6 Months Ended

Jun. 30, 2016

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

The following table summarizes the significant differences in income tax expense based on the differences between our effective tax rate and the federal statutory rate (in thousands):

	Three Months Ended June 30,
	2016					2015
Income Before Income Taxes	$	38,516				$	39,184
Income tax calculated at 35% federal statutory rate	13,481			35.0	%	13,715			35.0	%
Permanent or flow through adjustments:
State income, net of federal provisions	(1,025		)	(2.7	)	367			0.9
Flow-through repairs deductions	(6,971		)	(18.1	)	(4,848		)	(12.4	)
Production tax credits	(2,324		)	(6.0	)	(651		)	(1.7	)
Plant and depreciation of flow through items	(246		)	(0.6	)	(245		)	(0.6	)
Prior year permanent return to accrual adjustments	(128		)	(0.3	)	—			—
Other, net	160			0.4		(127		)	(0.2	)
	(10,534		)	(27.3	)	(5,504		)	(14.0	)
Income Tax Expense	$	2,947		7.7	%	$	8,211		21.0	%

	Six Months Ended June 30,
	2016					2015
Income Before Income Taxes	$	79,042				$	100,625
Income tax calculated at 35% federal statutory rate	27,665			35.0	%	35,219			35.0	%
Permanent or flow through adjustments:
State income, net of federal provisions	(2,125		)	(2.6	)	528			0.6
Flow-through repairs deductions	(13,645		)	(17.3	)	(14,461		)	(14.4	)
Production tax credits	(5,099		)	(6.5	)	(1,912		)	(1.9	)
Plant and depreciation of flow through items	(1,184		)	(1.5	)	(626		)	(0.6	)
Prior year permanent return to accrual adjustments	(128		)	(0.2	)	—			—
Other, net	(65		)	—		(521		)	(0.6	)
	(22,246		)	(28.1	)	(16,992		)	(16.9	)
Income Tax Expense	$	5,419		6.9	%	$	18,227		18.1	%