Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Liabilities:
Kolltan acquisition contingent consideration	$ 7,587	$ 12,485
Fair value | Level 3
Liabilities:
Kolltan acquisition contingent consideration	7,587	12,485
Fair Value Measurements. | Level 2
Assets:
Money market funds and cash equivalents	54,597	4,024
Marketable securities	138,888	53,151
Total financial assets at fair value	193,485	57,175
Fair Value Measurements. | Level 3
Liabilities:
Kolltan acquisition contingent consideration	7,587	12,485
Total financial liabilities at fair value	7,587	12,485
Fair Value Measurements. | Fair value
Assets:
Money market funds and cash equivalents	54,597	4,024
Marketable securities	138,888	53,151
Total financial assets at fair value	193,485	57,175
Liabilities:
Kolltan acquisition contingent consideration	7,587	12,485
Total financial liabilities at fair value	$ 7,587	$ 12,485