Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Liabilities:
Kolltan acquisition contingent consideration	$ 8,267	$ 12,485
Fair value | Level 3
Liabilities:
Kolltan acquisition contingent consideration	8,267	12,485
Fair Value Measurements. | Level 2
Assets:
Money market funds and cash equivalents	35,066	4,024
Marketable securities	150,586	53,151
Total financial assets at fair value	185,652	57,175
Fair Value Measurements. | Level 3
Liabilities:
Kolltan acquisition contingent consideration	8,267	12,485
Total financial liabilities at fair value	8,267	12,485
Fair Value Measurements. | Fair value
Assets:
Money market funds and cash equivalents	35,066	4,024
Marketable securities	150,586	53,151
Total financial assets at fair value	185,652	57,175
Liabilities:
Kolltan acquisition contingent consideration	8,267	12,485
Total financial liabilities at fair value	$ 8,267	$ 12,485