Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 69,886	$ 59,321
Cash
Assets
Cash and cash equivalents	34,726	20,448
Money market
Assets
Cash and cash equivalents	35,160	38,873
Domestic corporate commercial paper
Assets
Cash and cash equivalents	0	0
Recurring basis | Estimated Fair Value
Assets
Cash and cash equivalents	69,886	59,321
Marketable securities	91,015	177,140
Recurring basis | Domestic corporate debt securities | Estimated Fair Value
Assets
Marketable securities	41,229	132,356
Recurring basis | Domestic corporate commercial paper | Estimated Fair Value
Assets
Marketable securities	24,905	0
Recurring basis | Agency bonds | Estimated Fair Value
Assets
Marketable securities	12,389	44,784
Recurring basis | US treasury bonds | Estimated Fair Value
Assets
Marketable securities	12,492
Recurring basis | Cash | Estimated Fair Value
Assets
Cash and cash equivalents	34,726	20,448
Recurring basis | Money market | Estimated Fair Value
Assets
Cash and cash equivalents	35,160	38,873
Recurring basis | Domestic corporate commercial paper | Estimated Fair Value
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 1
Assets
Cash and cash equivalents	69,886	59,321
Marketable securities	0	0
Recurring basis | Level 1 | Domestic corporate debt securities
Assets
Marketable securities	0	0
Recurring basis | Level 1 | Domestic corporate commercial paper
Assets
Marketable securities	0	0
Recurring basis | Level 1 | Agency bonds
Assets
Marketable securities		0
Recurring basis | Level 1 | US treasury bonds
Assets
Marketable securities	0
Recurring basis | Level 1 | Cash
Assets
Cash and cash equivalents	34,726	20,448
Recurring basis | Level 1 | Money market
Assets
Cash and cash equivalents	35,160	38,873
Recurring basis | Level 1 | Domestic corporate commercial paper
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 2
Assets
Cash and cash equivalents	0	0
Marketable securities	91,015	177,140
Recurring basis | Level 2 | Domestic corporate debt securities
Assets
Marketable securities	41,229	132,356
Recurring basis | Level 2 | Domestic corporate commercial paper
Assets
Marketable securities	24,905	0
Recurring basis | Level 2 | Agency bonds
Assets
Marketable securities	12,389	44,784
Recurring basis | Level 2 | US treasury bonds
Assets
Marketable securities	12,492
Recurring basis | Level 2 | Cash
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 2 | Money market
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 2 | Domestic corporate commercial paper
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 3
Assets
Cash and cash equivalents	0	0
Marketable securities	0	0
Recurring basis | Level 3 | Domestic corporate debt securities
Assets
Marketable securities	0	0
Recurring basis | Level 3 | Domestic corporate commercial paper
Assets
Marketable securities	0	0
Recurring basis | Level 3 | Agency bonds
Assets
Marketable securities		0
Recurring basis | Level 3 | US treasury bonds
Assets
Marketable securities	0
Recurring basis | Level 3 | Cash
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 3 | Money market
Assets
Cash and cash equivalents	0	0
Recurring basis | Level 3 | Domestic corporate commercial paper
Assets
Cash and cash equivalents	$ 0	$ 0