Fair Value Measurements - Carrying Value and Fair Value of Certain Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 25,028	$ 7,703
Long-term restricted cash equivalents	25	500
Marketable securities - held-to-maturity		37,955
Debt instrument, fair value		5,060
Carrying Value [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		21,473
Carrying Value [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		16,482
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	25,028	7,703
Long-term restricted cash equivalents	25	500
Marketable securities - held-to-maturity		37,955
Debt instrument, fair value		0
Estimate of Fair Value Measurement [Member] | Level 1 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		21,473
Estimate of Fair Value Measurement [Member] | Level 1 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		16,482
Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Long-term restricted cash equivalents	0	0
Marketable securities - held-to-maturity		0
Debt instrument, fair value		0
Estimate of Fair Value Measurement [Member] | Level 2 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		0
Estimate of Fair Value Measurement [Member] | Level 2 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		0
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Long-term restricted cash equivalents	$ 0	0
Marketable securities - held-to-maturity		0
Debt instrument, fair value		5,060
Estimate of Fair Value Measurement [Member] | Level 3 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		0
Estimate of Fair Value Measurement [Member] | Level 3 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities - held-to-maturity		$ 0