Investments and Fair Value of Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands |
9 Months Ended |
|
Sep. 30, 2019 |
Dec. 31, 2018 |
| Marketable securities |
|
|
| Amortized Cost |
$ 214,912
|
$ 97,016
|
| Gross Unrealized Gains |
174
|
|
| Gross Unrealized Losses |
(8)
|
(29)
|
| Fair Value |
215,078
|
96,987
|
| Assets: |
|
|
| Investments |
215,078
|
96,987
|
| Transfers between Level 1, Level 2 or Level 3 |
|
|
| Transfer from Level 1 to Level 2, assets |
0
|
|
| Transfer from Level 2 to Level 1, assets |
0
|
|
| Transfers into Level 3, assets |
0
|
|
| Transfer out of Level 3, assets |
0
|
|
| Transfer from Level 1 to Level 2, liabilities |
0
|
|
| Transfer from Level 2 to Level 1, liabilities |
0
|
|
| Transfers into Level 3, liabilities |
0
|
|
| Transfer out of Level 3, liabilities |
0
|
|
| U.S. treasury bills and notes |
|
|
| Marketable securities |
|
|
| Amortized Cost |
201,045
|
|
| Gross Unrealized Gains |
165
|
|
| Gross Unrealized Losses |
(8)
|
|
| Fair Value |
201,202
|
|
| Assets: |
|
|
| Investments |
201,202
|
|
| U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Amortized Cost |
13,867
|
17,704
|
| Gross Unrealized Gains |
9
|
|
| Gross Unrealized Losses |
|
(3)
|
| Fair Value |
13,876
|
17,701
|
| Assets: |
|
|
| Investments |
13,876
|
17,701
|
| U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Amortized Cost |
|
79,312
|
| Gross Unrealized Losses |
|
(26)
|
| Fair Value |
|
79,286
|
| Assets: |
|
|
| Investments |
|
79,286
|
| Recurring |
|
|
| Assets: |
|
|
| Assets |
324,689
|
404,051
|
| Recurring | Money market funds |
|
|
| Assets: |
|
|
| Cash equivalents |
109,611
|
282,160
|
| Recurring | U.S. treasury bills and notes |
|
|
| Marketable securities |
|
|
| Fair Value |
201,202
|
|
| Assets: |
|
|
| Investments |
201,202
|
|
| Recurring | U.S. treasury bills |
|
|
| Assets: |
|
|
| Cash equivalents |
|
24,904
|
| Recurring | U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Fair Value |
13,876
|
17,701
|
| Assets: |
|
|
| Investments |
13,876
|
17,701
|
| Recurring | U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Fair Value |
|
79,286
|
| Assets: |
|
|
| Investments |
|
79,286
|
| Recurring | Level 1 |
|
|
| Assets: |
|
|
| Assets |
109,611
|
282,160
|
| Recurring | Level 1 | Money market funds |
|
|
| Assets: |
|
|
| Cash equivalents |
109,611
|
282,160
|
| Recurring | Level 2 |
|
|
| Assets: |
|
|
| Assets |
215,078
|
121,891
|
| Recurring | Level 2 | U.S. treasury bills and notes |
|
|
| Marketable securities |
|
|
| Fair Value |
201,202
|
|
| Assets: |
|
|
| Investments |
201,202
|
|
| Recurring | Level 2 | U.S. treasury bills |
|
|
| Assets: |
|
|
| Cash equivalents |
|
24,904
|
| Recurring | Level 2 | U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Fair Value |
13,876
|
17,701
|
| Assets: |
|
|
| Investments |
$ 13,876
|
17,701
|
| Recurring | Level 2 | U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Fair Value |
|
79,286
|
| Assets: |
|
|
| Investments |
|
$ 79,286
|