Income Taxes Federal Statutory Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income before income taxes	$ 32,081	$ 48,832	$ 96,493
Income Tax Statutory Rate Reconciliation [Abstract]
“Expected” federal income tax	6,737	10,255	33,773
Increase (decrease) in taxes attributable to:
State taxes, net of federal income tax benefit	2,251	3,420	4,986
Uncertain tax positions	323	24	12
Property flow-through	(2,054)	(839)	(1,027)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount	5,350	0	0
Tax reform - rate change impact on deferred taxes	77	0	(2,357)
Reversal of excess deferred taxes recognized in regulatory liability	(2,355)	(1,383)	0
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Pensions	(1,244)	0	0
Stock-based compensation	(223)	(1,602)	(552)
Other items, net	(408)	190	558
Income Tax Expense (Benefit)	$ 8,454	$ 10,065	$ 35,393