Fair Value Measurement - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 05, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	May. 11, 2015	May. 10, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured with fair value		$ 141,425,000		$ 141,425,000
Preferred stock liquidation preference per share		$ 10.00		$ 10.00
Preferred stock dividend rate				3.00%
Common stock, par value		$ 0.00001		$ 0.00001		$ 0.00001	$ 0.00001	$ 0.00001
Net (loss) income		$ (73,483,000)	$ 17,322,000	$ (67,982,000)	$ 13,942,000	$ 3,070,000
Minimum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net loss				$ 57,800,000
Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net loss				$ 51,900,000
Initial Conversion Price
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Common stock, par value		$ 2.25		$ 2.25
Floor Price
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Common stock, par value		$ 1.75		$ 1.75
Volatility Assumption [Member] | Minimum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net loss				$ 12,400,000
Volatility Assumption [Member] | Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net loss				$ 12,600,000
Transaction Occurring Assumption [Member] | Minimum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net loss				$ 15,700,000
Transaction Occurring Assumption [Member] | Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net loss				$ 15,700,000
Series B Preferred Stock [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Capital	$ 600,000,000
Convertible preferred stock, shares issued	600,000	600,000		600,000		0
Preferred stock liquidation preference per share	$ 1,000
Preferred stock dividend rate	3.00%
Common stock, par value		$ 1.75		$ 1.75
Series B Preferred Stock [Member] | Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Common stock, par value		$ 2.25		$ 2.25
Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured with fair value						$ 0