Convertible and Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			6 Months Ended	12 Months Ended
	Jun. 30, 2015	Jun. 11, 2015	Jun. 30, 2015	Dec. 31, 2014
Temporary Equity [Line Items]
Percentage of accrued but unpaid dividends paid in shares		50.00%
Percentage of accrued but unpaid dividends forfeited		50.00%
Share price, accrued dividend in shares		$ 5.215
Cumulative unpaid accruing dividends in arrears	$ 18.5		$ 18.5	$ 14.4
Exercise put options period		120 days
Series B-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Number of shares issued upon exercise of stock warrants	86,028		86,028
Cumulative unpaid accruing dividends in arrears	$ 1.7		$ 1.7	1.5
Accruing dividends	$ 0.9		$ 0.9
Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Number of shares issued upon exercise of stock warrants	5,247		5,247
Cumulative unpaid accruing dividends in arrears	$ 1.6		$ 1.6	1.1
Issuable common stock to redeemable convertible preferred stockholders	155,273		155,273
Series D Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Cumulative unpaid accruing dividends in arrears	$ 5.9		$ 5.9	3.4
Issuable common stock to redeemable convertible preferred stockholders	561,685		561,685
Series B and B-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Accruing dividends	$ 5.5		$ 5.5
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Cumulative unpaid accruing dividends in arrears	9.3		9.3	$ 8.4
Accruing dividends	$ 4.6		$ 4.6
Series C and D Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Issuable common stock to redeemable convertible preferred stockholders	716,958		716,958