Investments and Fair Value of Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands |
6 Months Ended |
|
Jun. 30, 2019 |
Dec. 31, 2018 |
| Marketable securities |
|
|
| Amortized Cost |
$ 220,956
|
$ 97,016
|
| Gross Unrealized Gains |
290
|
|
| Gross Unrealized Losses |
|
(29)
|
| Fair Value |
221,246
|
96,987
|
| Assets: |
|
|
| Investments |
221,246
|
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. government agency bonds |
|
|
| Marketable securities |
|
|
| Amortized Cost |
32,926
|
17,704
|
| Gross Unrealized Gains |
22
|
|
| Gross Unrealized Losses |
|
(3)
|
| Fair Value |
32,948
|
17,701
|
| Assets: |
|
|
| Investments |
32,948
|
17,701
|
| U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Amortized Cost |
188,030
|
79,312
|
| Gross Unrealized Gains |
268
|
|
| Gross Unrealized Losses |
|
(26)
|
| Fair Value |
188,298
|
79,286
|
| Assets: |
|
|
| Investments |
188,298
|
79,286
|
| Recurring |
|
|
| Assets: |
|
|
| Assets |
362,330
|
404,051
|
| Recurring | Money market funds |
|
|
| Assets: |
|
|
| Cash equivalents |
141,084
|
282,160
|
| Recurring | U.S. treasury bills |
|
|
| Marketable securities |
|
|
| Fair Value |
51,148
|
|
| Assets: |
|
|
| Cash equivalents |
|
24,904
|
| Investments |
51,148
|
|
| Recurring | U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Fair Value |
32,948
|
17,701
|
| Assets: |
|
|
| Investments |
32,948
|
17,701
|
| Recurring | U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Fair Value |
137,150
|
79,286
|
| Assets: |
|
|
| Investments |
137,150
|
79,286
|
| Recurring | Level 1 |
|
|
| Assets: |
|
|
| Assets |
141,084
|
282,160
|
| Recurring | Level 1 | Money market funds |
|
|
| Assets: |
|
|
| Cash equivalents |
141,084
|
282,160
|
| Recurring | Level 2 |
|
|
| Assets: |
|
|
| Assets |
221,246
|
121,891
|
| Recurring | Level 2 | U.S. treasury bills |
|
|
| Marketable securities |
|
|
| Fair Value |
51,148
|
|
| Assets: |
|
|
| Cash equivalents |
|
24,904
|
| Investments |
51,148
|
|
| Recurring | Level 2 | U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Fair Value |
32,948
|
17,701
|
| Assets: |
|
|
| Investments |
32,948
|
17,701
|
| Recurring | Level 2 | U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Fair Value |
137,150
|
79,286
|
| Assets: |
|
|
| Investments |
$ 137,150
|
$ 79,286
|