Components of Prepaid Expenses and Other (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Prepaid Expenses [Line Items]
Prepaid expenses and other, current	$ 12,600	$ 13,259
Prepaid expenses and other, long-term	2,777	1,999
Totals	15,377	15,258
CRO services
Prepaid Expenses [Line Items]
Prepaid expenses and other, current	3,642	4,810
Prepaid expenses and other, long-term	702	400
Other clinical development
Prepaid Expenses [Line Items]
Prepaid expenses and other, current	3,208	2,043
Prepaid expenses and other, long-term	341	468
Insurance
Prepaid Expenses [Line Items]
Prepaid expenses and other, current	1,547	3,452
Professional fees
Prepaid Expenses [Line Items]
Prepaid expenses and other, current	1,476	544
Other
Prepaid Expenses [Line Items]
Prepaid expenses and other, current	2,727	2,410
Prepaid expenses and other, long-term	$ 1,734	$ 1,131