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Summary of Significant Accounting Policies (Details)
 12 Months Ended
Dec. 31, 2014
Cash equivalents:  
Maximum original maturity period of highly liquid debt instruments to be considered as cash equivalents 3 months
TNCLP  
Consolidation and Noncontrolling Interest  
Ownership interest (as a percent) 75.30%us-gaap_MinorityInterestOwnershipPercentageByParent
/ dei_LegalEntityAxis
= us-gaap_PartnershipInterestMember
Percentage of ownership interest held by outside investors 24.70%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ dei_LegalEntityAxis
= us-gaap_PartnershipInterestMember