Preferred Stock - Assumptions Used to Estimate Fair Value of Embedded Redemption Derivative Financial Instrument (Detail)	Dec. 31, 2017
Expected Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated fair value assumptions	59.60
Incremental Borrowing Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated fair value assumptions	12.00
Risk Free Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated fair value assumptions	1.59