Quarterly report pursuant to Section 13 or 15(d)

Intangible Assets - Summary of Intangible Assets (Detail)

v3.10.0.1
Intangible Assets - Summary of Intangible Assets (Detail) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Sep. 30, 2018
Mar. 31, 2018
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 9,100
Intangibles not subject to amortization, Net Carrying Amount 3,700 3,700
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 1,700
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 2,000
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 1,402 1,312
Intangibles subject to amortization, Net Carrying Amount $ 1,298 $ 1,388