Basis of Presentation and Summary of Significant Accounting Policies - Natural Gas Imbalances (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Current Assets
Gas Balance Arrangements [Line Items]
Gas balancing receivable (payable)	$ 0.9	$ 0.7
Other Current Liabilities
Gas Balance Arrangements [Line Items]
Gas balancing receivable (payable)	$ (0.1)	$ (0.3)

The value of gas balancing asset or liability as of the end of the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 10
-Section S99
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=50486907&loc=d3e512571-122862

Name:	us-gaap_GasImbalanceAssetLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant