Divestitures - Assets and Liabilities in Disposal (Details) - Discontinued Operations, Held-for-sale - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Property, plant and equipment, net	$ 719,584	$ 0
Liabilities:
Other current liabilities	4,763	0
Other liabilities and credits	$ 190,541	$ 0

Amount classified as other liabilities attributable to disposal group held for sale or disposed of, expected to be disposed of within one year or the normal operating cycle, if longer.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant