Carrying value as of the balance sheet date of the portion of long-term debt due within one year or the operating cycle if longer identified as Convertible Notes Payable. Convertible Notes Payable is a written promise to pay a note which can be exchanged for a specified amount of another, related security, at the option of the issuer and the holder.

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Redeemable Convertible Notes - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Aug. 19, 2015
Debt Instrument [Line Items]
Redeemable convertible notes, outstanding balance	$ 0	$ 5,085,000
Derivative liability	$ 0
Convertible Notes
Debt Instrument [Line Items]
Convertible notes, total outstanding principal amount			$ 37,000,000
Convertible notes, maturity date	Feb. 19, 2018
Derivative liability	$ 0
Convertible Notes \| After Reverse Stock Split
Debt Instrument [Line Items]
Redeemable convertible notes, conversion per share price	$ 137.85