Marketable Securities - Schedule of available-for-sale marketable securities and cash and cash equivalents (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents, amortized cost value	$ 69,886,000	$ 59,321,000
Cash and cash equivalents, fair value	69,886,000	59,321,000
Marketable securities, amortized cost	91,012,000	177,895,000
Available-for-sale securities, gross unrealized gains	9,000.0	0.0
Available-for-sale securities, gross unrealized losses	(6,000.0)	(755,000)
Marketable securities, fair value	91,015,000	177,140,000
Domestic corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities, amortized cost	41,229,000	132,886,000
Available-for-sale securities, gross unrealized gains	3,000	0
Available-for-sale securities, gross unrealized losses	(3,000)	(530,000)
Marketable securities, fair value	41,229,000	132,356,000
Domestic corporate commercial paper
Debt Securities, Available-for-sale [Line Items]
Marketable securities, amortized cost	24,900,000	0
Available-for-sale securities, gross unrealized gains	5,000	0
Available-for-sale securities, gross unrealized losses	0	0
Marketable securities, fair value	24,905,000	0
Agency bonds
Debt Securities, Available-for-sale [Line Items]
Marketable securities, amortized cost	12,391,000	45,009,000
Available-for-sale securities, gross unrealized gains	1,000	0
Available-for-sale securities, gross unrealized losses	(3,000)	(225,000)
Marketable securities, fair value	12,389,000	44,784,000
US treasury bonds
Debt Securities, Available-for-sale [Line Items]
Marketable securities, amortized cost	12,492,000
Available-for-sale securities, gross unrealized gains	0
Available-for-sale securities, gross unrealized losses	0
Marketable securities, fair value	12,492,000
Cash
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents, amortized cost value	34,726,000	20,448,000
Cash and cash equivalents, fair value	34,726,000	20,448,000
Money market
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents, amortized cost value	35,160,000	38,873,000
Cash and cash equivalents, fair value	35,160,000	38,873,000
Domestic corporate commercial paper
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents, amortized cost value	0	0
Cash and cash equivalents, fair value	$ 0	$ 0

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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