Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Income tax benefit	$ 129	$ (3,850)	$ 199	$ (3,850)
Unrealized gains (losses) on available-for-sale debt securities, income tax expense	300	$ 0	700	$ 0
Accrued income tax provision	564		564		$ 726
Accrued Expenses and Other Current Liabilities [Member]
Income Tax Disclosure [Line Items]
Accrued income tax provision	$ 500		$ 500