Summary of Significant Accounting Policies - Summary of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 184,090	$ 224,868
Nicox stock with lockup provisions	18	18
Total assets	184,108	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	184,090	224,868
Nicox stock with lockup provisions	0	0
Total assets	184,090	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	18	18
Total assets	18	$ 18
Nicox
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nicox stock with lockup provisions	$ 100