Balance Sheet Components Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Balance Sheet Components [Abstract]
Accrued taxes other than income taxes	$ 37,723	$ 33,802
Current unsettled interest rate swap derivative liabilities	0	34,447
Employee paid time off accruals	20,644	20,330
Accrued interest	30,343	16,351
Current portion of pensions and other postretirement benefits	10,036	11,544
Utility energy commodity derivative liabilities	6,853	8,848
Other current liabilities	27,805	33,791
Other current liabilities	$ 133,404	$ 159,113