Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019
Income Taxes [Line Items]
Income tax expense	$ 11,864	$ 11,481	$ 14,509	$ 15,068
Income tax expense increase (decrease)	400		(600)
Increase (decrease) in pre-tax net income	(6,600)
Ratepayer net refund	107,000		107,000
Unrecognized tax benefits	10,600	9,700	10,600	9,700
Tax benefits that, if recognized, would affect the effective tax rate	$ 3,100	$ 2,900	$ 3,100	$ 2,900
Scenario, Forecast
Income Taxes [Line Items]
Effective tax rate estimate					22.00%