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Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2017 | Mar. 31, 2018 | Mar. 31, 2017
Schedule Of Intangible Assets [Line Items] |  |  |
Intangibles not subject to amortization, Gross Carrying Amount |  | $ 12,800 | $ 12,800
Intangibles not subject to amortization, Impairment Loss |  | 9,100 |
Intangibles not subject to amortization, Net Carrying Amount |  | 3,700 | 12,800
Permits [Member] |  |  |
Schedule Of Intangible Assets [Line Items] |  |  |
Intangibles not subject to amortization, Gross Carrying Amount |  | 10,300 | 10,300
Intangibles not subject to amortization, Impairment Loss | $ 8,600 | 8,600 |
Intangibles not subject to amortization, Net Carrying Amount |  | 1,700 | 10,300
Tradename [Member] |  |  |
Schedule Of Intangible Assets [Line Items] |  |  |
Intangibles not subject to amortization, Gross Carrying Amount |  | 2,500 | 2,500
Intangibles not subject to amortization, Impairment Loss | $ 500 | 500 |
Intangibles not subject to amortization, Net Carrying Amount |  | 2,000 | 2,500
Customer Relationships [Member] |  |  |
Schedule Of Intangible Assets [Line Items] |  |  |
Intangibles subject to amortization, Gross Carrying Amount |  | 2,700 | 2,700
Intangibles subject to amortization, Accumulated Amortization |  | 1,312 | 1,132
Intangibles subject to amortization, Net Carrying Amount |  | $ 1,388 | $ 1,568

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- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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