Related Party Transactions (Details) - BGP Joint Venture [Member] - Co-venturer [Member] - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Property Subject to or Available for Operating Lease [Line Items]
Company's outstanding common stock owned by BGP, percent	14.40%
Related party transaction, revenues from transactions with related party	$ 4.9	$ 3.9
Receivables due from BGP	$ 1.1

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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