Derivative and Other Financial Instruments and Fair Value Measurements - Additional Information (Detail) $ / shares in Units, BTU in Trillions		1 Months Ended				12 Months Ended
	Jun. 11, 2010 USD ($) $ / shares shares	Apr. 30, 2016 shares	Sep. 30, 2015 shares	May 31, 2015 USD ($) shares	Jun. 30, 2010 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) BTU t $ / shares shares	Dec. 31, 2016 USD ($)	Jun. 30, 2015	Feb. 28, 2015 $ / shares
Derivatives
Cash collateral posted or held | $						$ 0
Amount subject to enforceable master netting arrangement not offset | $						$ 0	$ 0
Warrant issued to purchase common stock | shares	1,500,000				1,500,000
Aggregate purchase price of common stock warrant | $	$ 300,000				$ 300,000
Exercise price of warrants | $ / shares	$ 10.30				$ 10.30	$ 5.64			$ 5.64
Warrant vested upon issuance	20.00%
Common stock warrants vesting percentage on each anniversary date	20.00%
Common stock warrants percentage vested								100.00%
Common stock warrants expiration date	2020-06
Price per share of common stock issued | $ / shares									$ 5.64
Warrants exercised | shares				15,000
Warrants outstanding | shares						1,448,333
Warrants issued on cashless basis | shares		20,000	16,667	7,500
Proceeds from issuance of common stock for warrants exercised | $				$ 100,000
Redeemable Preferred Stock
Derivatives
Temporary equity redemption period						66 months	44 days
Credit spread adjustment percentage							15.00%
Maximum
Derivatives
Number of days financing receivable is estimated to be outstanding						30 days
Common Stock Warrant Liability
Derivatives
Valuation technique						Black-Scholes	Monte Carlo simulation
Volatility							47.10%
Expected term							3 years 4 months 24 days
Equity raise probability						0.00%	60.00%
Equity raise price discount assumption							15.00%
Equity raise probability of weighted average price on volume days							10 days
Currency Exchange Hedging
Derivatives
Currency derivative contracts outstanding | $						$ 0
Metal
Derivatives
Offsetting buy and sell derivative contracts outstanding | t						10,700.0
Natural Gas | Swap Contract | Long
Derivatives
Offsetting forward buy and sell derivative contracts outstanding | BTU						1.4
Warrants
Derivatives
Common stock issued, Shares | shares		7,552	6,969	9,360