Investments and Fair Value Measurements - Schedule of Assets Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets
Cash equivalents	$ 78,654	$ 4,876
Marketable investments	170,433	241,973
Level 1
Assets
Cash equivalents	62,537	2,179
Marketable investments	48,895	31,940
Level 2
Assets
Cash equivalents	16,117	2,697
Marketable investments	121,538	210,033
Level 3
Assets
Cash equivalents	0	0
Marketable investments	0	0
Certificates of deposit
Assets
Marketable investments	161	162
Certificates of deposit | Level 1
Assets
Marketable investments	0	0
Certificates of deposit | Level 2
Assets
Marketable investments	161	162
Certificates of deposit | Level 3
Assets
Marketable investments	0	0
U.S. treasury
Assets
Marketable investments	48,895	31,940
U.S. treasury | Level 1
Assets
Marketable investments	48,895	31,940
U.S. treasury | Level 2
Assets
Marketable investments	0	0
U.S. treasury | Level 3
Assets
Marketable investments	0	0
U.S. agency securities
Assets
Marketable investments	99,552	177,730
U.S. agency securities | Level 1
Assets
Marketable investments	0	0
U.S. agency securities | Level 2
Assets
Marketable investments	99,552	177,730
U.S. agency securities | Level 3
Assets
Marketable investments	0	0
Commercial paper
Assets
Marketable investments	12,553	15,240
Commercial paper | Level 1
Assets
Marketable investments	0	0
Commercial paper | Level 2
Assets
Marketable investments	12,553	15,240
Commercial paper | Level 3
Assets
Marketable investments	0	0
Municipal bonds
Assets
Marketable investments	6,392	3,015
Municipal bonds | Level 1
Assets
Marketable investments	0	0
Municipal bonds | Level 2
Assets
Marketable investments	6,392	3,015
Municipal bonds | Level 3
Assets
Marketable investments	0	0
Corporate bonds
Assets
Marketable investments	2,880	13,886
Corporate bonds | Level 1
Assets
Marketable investments	0	0
Corporate bonds | Level 2
Assets
Marketable investments	2,880	13,886
Corporate bonds | Level 3
Assets
Marketable investments	0	0
Money market funds
Assets
Cash equivalents	41,038	2,179
Money market funds | Level 1
Assets
Cash equivalents	41,038	2,179
Money market funds | Level 2
Assets
Cash equivalents	0	0
Money market funds | Level 3
Assets
Cash equivalents	0	0
U.S. treasury
Assets
Cash equivalents	21,499
U.S. treasury | Level 1
Assets
Cash equivalents	21,499
U.S. treasury | Level 2
Assets
Cash equivalents	0
U.S. treasury | Level 3
Assets
Cash equivalents	0
Commercial paper
Assets
Cash equivalents		2,697
Commercial paper | Level 1
Assets
Cash equivalents		0
Commercial paper | Level 2
Assets
Cash equivalents		2,697
Commercial paper | Level 3
Assets
Cash equivalents		$ 0
Municipal bonds
Assets
Cash equivalents	15,867
Municipal bonds | Level 1
Assets
Cash equivalents	0
Municipal bonds | Level 2
Assets
Cash equivalents	15,867
Municipal bonds | Level 3
Assets
Cash equivalents	0
Corporate bonds
Assets
Cash equivalents	250
Corporate bonds | Level 1
Assets
Cash equivalents	0
Corporate bonds | Level 2
Assets
Cash equivalents	250
Corporate bonds | Level 3
Assets
Cash equivalents	$ 0