Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 24	$ 1,034
Accrued goods and services	694	2,082
Accrued clinical trial costs	1,354	1,683
Accrued drug purchase costs	371	4,245
Accrued payroll and related benefits	44	2,315
Accrued restructuring expenses	1,056	921	$ 628
Income taxes payable	83	83
Deferred tax incentives	1,314	1,314
Total accounts payable, accrued expenses and other	$ 4,940	$ 13,677