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Environmental Settlement and Related Costs - Additional Information (Detail) (USD $)
 0 Months Ended 3 Months Ended 9 Months Ended 0 Months Ended
Aug. 25, 2014
Sep. 30, 2014
Sep. 30, 2014
Oct. 01, 2014
Charge
Environmental Exit Cost [Line Items]        
Fines associated with the Consent Decree amount $ 3,000,000us-gaap_EnvironmentalRemediationExpense $ 6,600,000us-gaap_EnvironmentalRemediationExpense $ 6,600,000us-gaap_EnvironmentalRemediationExpense  
Preliminarily estimated cost of restoration 3,000,000us-gaap_EnvironmentalExitCostsReasonablyPossibleAdditionalLoss      
Maximum cost of restoration 9,000,000us-gaap_EnvironmentalExitCostsReasonablyPossibleAdditionalLossesHighEstimate      
Subsequent Event [Member]        
Environmental Exit Cost [Line Items]        
Fine agreed to pay for violation of the Clean Water Act       $ 600,000teng_FinesForFailureToComplyWithEnvironmentalProtectionRequirements
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Period of probation       2 years
Number of misdemeanor charges to which the company pleaded guilty       3teng_NumberOfCharges
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember