Environmental Settlement and Related Costs - Additional Information (Detail) |
Apr. 08, 2016
USD ($)
|
Jul. 20, 2015
USD ($)
|
Oct. 01, 2014
USD ($)
Charge
|
Apr. 21, 2017
USD ($)
|
Aug. 25, 2014
USD ($)
Installment
|
|---|---|---|---|---|---|
| Environmental Exit Cost [Line Items] | |||||
| Fine agreed to pay for violation of the Clean Water Act | $ 600,000 | ||||
| Period of probation | 2 years | ||||
| Number of misdemeanor charges to which the company pleaded guilty | Charge | 3 | ||||
| Civil penalties per violation | $ 3,000,000 | ||||
| Number of installments for payment of civil penalty | Installment | 2 | ||||
| Estimated site restoration costs | $ 13,000,000 | ||||
| First Installment [Member] | |||||
| Environmental Exit Cost [Line Items] | |||||
| Civil penalty payment plus interest | $ 1,000,000 | ||||
| Subsequent Event [Member] | Second Installment [Member] | |||||
| Environmental Exit Cost [Line Items] | |||||
| Civil penalty payment plus interest | $ 250,000 | ||||
| Scenario, Forecast [Member] | Third Installment [Member] | |||||
| Environmental Exit Cost [Line Items] | |||||
| Civil penalty payment due plus interest | $ 1,750,000 |