Summary of Significant Accounting Policies - Summary of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 205,542	$ 224,868
Nicox stock with lockup provisions	16	18
Total assets	205,558	224,886
Recurring Measurements | Quoted Prices in Active Markets for Identical Items (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	205,542	224,868
Nicox stock with lockup provisions	0	0
Total assets	205,542	224,868
Recurring Measurements | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Nicox stock with lockup provisions	0	0
Total assets	0	0
Recurring Measurements | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Nicox stock with lockup provisions	16	18
Total assets	$ 16	$ 18