Commitments and Contingencies - Additional Information (Details) ft² in Thousands, $ in Thousands	1 Months Ended	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended		24 Months Ended
	Jul. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) officer	Jan. 01, 2019 USD ($)	May 31, 2018 ft²	Aug. 31, 2015 ft²
Commitments And Contingencies [Line Items]
Weighted average discount rate, operating lease liabilities		9.85%												9.85%		9.85%
Weighted average remaining lease term, operating leases		6 years 6 months												6 years 6 months		6 years 6 months
Rentable square feet of facility space | ft²																			51,000
Optional term of extending lease agreement																			5 years
Current contractual base rent payments per month														$ 95
Percentage of increase in annual rental payments														3.00%
Property and equipment, net		$ 10,506	$ 10,569	$ 11,054	$ 11,657	$ 15,868	$ 16,129	$ 16,327	$ 16,474	$ 11,054	$ 16,327	$ 10,569	$ 16,129	$ 10,506	$ 15,868	$ 10,506
Facility lease obligation		0				7,998	7,998	7,998	7,998		7,998		7,998	0	7,998	0
Interest expense		1	0	1	0	262	$ 262	$ 261	$ 262	1	$ 523	1	$ 785	2	1,047
Property and equipment, gross		16,185				20,456								16,185	20,456	16,185
Right-of-use lease assets capitalized		1,833	$ 1,837	$ 1,837	$ 1,833	0				$ 1,837		$ 1,837		1,833	0	1,833
Lease liabilities capitalized		6,262												6,262		$ 6,262
Rent expense associated with primary facility lease (Topic 842)														880
Right of use assets obtained in exchange for lease liabilities														1,827	0
Three Former Officers
Commitments And Contingencies [Line Items]
Number of former officers | officer																3
Severance expenses														878	332
Stock compensation expense related to accelerated vesting of former officers stock options														0	212
November 2018 Employee Restructuring
Commitments And Contingencies [Line Items]
Accrued severance costs		52												52		$ 52
Severance costs expensed during the period														67	196
Sublease Agreement
Commitments And Contingencies [Line Items]
Sublease term	3 years
Monthly rental income	$ 12
ASU 2016-02 (Topic 842)
Commitments And Contingencies [Line Items]
Facility lease obligation																	$ 7,998
Right-of-use lease assets capitalized																	1,827
Lease liabilities capitalized																	6,786
Accrued Compensation | Three Former Officers
Commitments And Contingencies [Line Items]
Accrued severance costs		33												$ 33		33
Building Related to Facility Lease Obligation
Commitments And Contingencies [Line Items]
Property and equipment, estimated useful life														25 years
Property and equipment, net						10,557									10,557
Building Related to Facility Lease Obligation | ASU 2016-02 (Topic 842)
Commitments And Contingencies [Line Items]
Property and equipment, gross																	10,557
Primary Facility Lease
Commitments And Contingencies [Line Items]
Grounds rent expense per month														$ 8
Facility lease obligation						7,998									7,998
Interest expense															1,044
Rent expense associated with primary facility lease (Topic 840)															308
Primary Facility Lease | Sublease Agreement
Commitments And Contingencies [Line Items]
Rentable square feet of facility space | ft²																		6,400
Primary Facility Lease | Other Accrued Expenses
Commitments And Contingencies [Line Items]
Accrued interest						41									41
Leasehold improvements
Commitments And Contingencies [Line Items]
Property and equipment, gross		$ 7,068				$ 1,168								$ 7,068	$ 1,168	$ 7,068
Leasehold improvements | ASU 2016-02 (Topic 842)
Commitments And Contingencies [Line Items]
Property and equipment, gross																	5,885
Cumulative Effect, Period of Adoption, Adjustment
Commitments And Contingencies [Line Items]
Increase to accumulated deficit																	714
Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-02 (Topic 842)
Commitments And Contingencies [Line Items]
Increase to accumulated deficit																	$ 714