Accounting Pronouncements Accounting Pronouncements (Details) - Accounting Standards Update 2017-07 - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Operating and Maintenance Expense
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net periodic benefit cost (credit)	$ 700	$ 2,000
Other Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net periodic benefit cost (credit)	$ (700)	$ (2,000)