Fair Value Measurement - Fair Value of Assets Measured on a Non-recurring Basis (Detail) - Fair Value, Measurements, Nonrecurring $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants, fair value	$ 2,840
Total Gains (Losses)	0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants, fair value	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants, fair value	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants, fair value	$ 2,840