Investments and Fair Value Measurements - Cash, Cash Equivalent and Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 22,501	$ 16,142	$ 21,355
Marketable securities	94,084	114,967
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Marketable securities	9,024	17,470
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Marketable securities	2,498	5,481
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities	68,713	78,160
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities	13,849	13,856
Cash
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	8,503	11,623
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	13,998	2,020
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 0	$ 2,499