Annual report pursuant to Section 13 and 15(d)

Intangible Assets - Summary of Intangible Assets (Detail)

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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