Derivative and Other Financial Instruments and Fair Value Measurements - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) BTU t	Dec. 31, 2014
Derivative [Line Items]
Cash collateral posted or held	$ 0
Amount subject to enforceable master netting arrangement not offset	$ 0
Derivative contracts | t	32,400
Redeemable Preferred Stock
Derivative [Line Items]
Preferred stock redemption period	66 months
Credit spread adjustment percentage	13.10%
Natural Gas | Swap Contract One
Derivative [Line Items]
Swap contracts | BTU	0
Common Stock Warrant Liability
Derivative [Line Items]
Valuation technique	Monte Carlo Simulation
Volatility	51.00%
Expected term	4 years 10 months 24 days	5 years 9 months 18 days
Equity raise probability	25.00%
Equity raise price discount assumption	15.00%