Fair Value of Financial Instruments - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Short-term investments:
Corporate commercial paper, bonds and notes	$ 6	$ 5,113
Corporate commercial paper, bonds and notes
Short-term investments:
Corporate commercial paper, bonds and notes	6	5,113
Fair Value, Measurements, Recurring
Short-term investments:
Total assets at fair value	10,274	16,737
Fair Value, Measurements, Recurring | Corporate commercial paper, bonds and notes
Short-term investments:
Corporate commercial paper, bonds and notes	6	5,113
Fair Value, Measurements, Recurring | Money market funds
Cash equivalents:
Cash equivalents	10,268	10,684
Fair Value, Measurements, Recurring | US government obligations
Cash equivalents:
Cash equivalents		550
Fair Value, Measurements, Recurring | Commercial paper
Cash equivalents:
Cash equivalents		300
Fair Value, Measurements, Recurring | Municipal bonds
Cash equivalents:
Cash equivalents		90
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Short-term investments:
Total assets at fair value	10,268	10,684
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Corporate commercial paper, bonds and notes
Short-term investments:
Corporate commercial paper, bonds and notes	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Money market funds
Cash equivalents:
Cash equivalents	10,268	10,684
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | US government obligations
Cash equivalents:
Cash equivalents		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Commercial paper
Cash equivalents:
Cash equivalents		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Municipal bonds
Cash equivalents:
Cash equivalents		0
Fair Value, Measurements, Recurring | Other Observable Inputs (Level 2)
Short-term investments:
Total assets at fair value	6	6,053
Fair Value, Measurements, Recurring | Other Observable Inputs (Level 2) | Corporate commercial paper, bonds and notes
Short-term investments:
Corporate commercial paper, bonds and notes	6	5,113
Fair Value, Measurements, Recurring | Other Observable Inputs (Level 2) | Money market funds
Cash equivalents:
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Other Observable Inputs (Level 2) | US government obligations
Cash equivalents:
Cash equivalents		550
Fair Value, Measurements, Recurring | Other Observable Inputs (Level 2) | Commercial paper
Cash equivalents:
Cash equivalents		300
Fair Value, Measurements, Recurring | Other Observable Inputs (Level 2) | Municipal bonds
Cash equivalents:
Cash equivalents		90
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3)
Short-term investments:
Total assets at fair value	0	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Corporate commercial paper, bonds and notes
Short-term investments:
Corporate commercial paper, bonds and notes	0	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Money market funds
Cash equivalents:
Cash equivalents	$ 0	0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | US government obligations
Cash equivalents:
Cash equivalents		0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Commercial paper
Cash equivalents:
Cash equivalents		0
Fair Value, Measurements, Recurring | Unobservable Inputs (Level 3) | Municipal bonds
Cash equivalents:
Cash equivalents		$ 0