Investments and Fair Value Measurements - Available-For-Sale Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 114,870	$ 46,703
Gross Unrealized Gain	98	0
Gross Unrealized Loss	(1)	(24)
Fair Value	114,967	46,679
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,462	12,867
Gross Unrealized Gain	9	0
Gross Unrealized Loss	(1)	(15)
Fair Value	17,470	12,852
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,481	20,086
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	5,481	20,086
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	78,075	5,933
Gross Unrealized Gain	85	0
Gross Unrealized Loss	0	(1)
Fair Value	78,160	5,932
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	13,852	7,817
Gross Unrealized Gain	4	0
Gross Unrealized Loss	0	(8)
Fair Value	$ 13,856	$ 7,809