Fair Value of Financial Instruments - Summary of Changes in Fair Value of Level 1 and Level 3 Financial Instruments (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) shares
Purchase price contingent liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of period	$ 5,649
Change in value of liabilities	206
Balance at end of period	$ 5,855
Series A Warrant Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the end of period, in shares | shares	485,121
Series A Warrant Liability [Member] | Common stock warrant liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of period	$ 49
Balance at the beginning of period, in shares | shares	485,121
Change in value of liabilities	$ 24
Balance at end of period	$ 73
Balance at the end of period, in shares | shares	485,121
Series C Warrant [Member] | Common stock warrant liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of period, in shares | shares	118,083
Balance at the end of period, in shares | shares	118,083
2017 PIPE Warrant Liability [Member] | Common stock warrant liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of period	$ 4,563
Balance at the beginning of period, in shares | shares	6,024,425
Change in value of liabilities	$ 1,711
Balance at end of period	$ 6,274
Balance at the end of period, in shares | shares	6,024,425
2018 PIPE Warrant Liability [Member] | Common stock warrant liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of period	$ 600
Balance at the beginning of period, in shares | shares	513,617
Change in value of liabilities	$ 184
Balance at end of period	$ 784
Balance at the end of period, in shares | shares	513,617