Commitments and Contingencies - New Mexico Audits (Details) - USD ($)	Sep. 30, 2018	Apr. 15, 2016	Aug. 31, 2014
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	$ 24,000,000	$ 189,000	$ 129,700

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
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Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant