Fair Value Measurements - Carrying Value and Fair Value of Certain Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 44,592	$ 7,703
Long-term restricted cash equivalents	525	500
Debt Securities, Trading	306
Marketable securities—held-to-maturity:	32,905	37,955
Credit facility repayment feature liability	7,069	5,060
Estimate of Fair Value Measurement [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	44,592	7,703
Long-term restricted cash equivalents	525	500
Debt Securities, Trading	306
Marketable securities—held-to-maturity:	32,905	37,955
Credit facility repayment feature liability	0	0
Estimate of Fair Value Measurement [Member] | Level 2
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
Debt Securities, Trading	0
Marketable securities—held-to-maturity:	0	0
Credit facility repayment feature liability	0	0
Estimate of Fair Value Measurement [Member] | Level 3
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
Debt Securities, Trading	0
Marketable securities—held-to-maturity:	0	0
Credit facility repayment feature liability	$ 7,069	$ 5,060