Fair Value Measurements (Details) - Measured on a recurring basis - USD ($)
$ in Thousands |
Dec. 31, 2018 |
Dec. 31, 2017 |
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
$ 93,239
|
$ 85,918
|
| Fair Value, assets |
93,189
|
85,856
|
| Unrealized Gains, assets |
1
|
|
| Unrealized Losses, assets |
(51)
|
(62)
|
| Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
29,761
|
| Fair Value, assets |
40,395
|
|
| Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, assets |
52,794
|
44,057
|
| Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, assets |
|
12,038
|
| Cash |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
30,501
|
24,367
|
| Adjusted Cost, assets |
30,501
|
24,367
|
| Cash | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
30,501
|
24,367
|
| Level 1 |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
17,323
|
14,454
|
| Fair Value, assets |
17,309
|
14,441
|
| Unrealized Losses, assets |
(14)
|
(13)
|
| Level 1 | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, assets |
6,903
|
5,394
|
| Level 1 | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, assets |
10,406
|
4,098
|
| Level 1 | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, assets |
|
4,949
|
| Level 1 | Money market funds |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
6,903
|
5,394
|
| Adjusted Cost, assets |
6,903
|
5,394
|
| Level 1 | Money market funds | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
6,903
|
5,394
|
| Level 1 | U.S. government notes |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
10,420
|
9,060
|
| Unrealized Losses, available-for-sale securities |
(14)
|
(13)
|
| Fair Value, available-for-sale investments |
10,406
|
9,047
|
| Level 1 | U.S. government notes | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
10,406
|
4,098
|
| Level 1 | U.S. government notes | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
4,949
|
| Level 2 |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
45,415
|
47,097
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
(37)
|
(49)
|
| Fair Value, available-for-sale investments |
45,379
|
47,048
|
| Level 2 | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,991
|
|
| Level 2 | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
42,388
|
39,959
|
| Level 2 | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
7,089
|
| Level 2 | Corporate bonds |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
21,612
|
24,943
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
(37)
|
(49)
|
| Fair Value, available-for-sale investments |
21,576
|
24,894
|
| Level 2 | Corporate bonds | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
21,576
|
17,805
|
| Level 2 | Corporate bonds | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
7,089
|
| Level 2 | Commercial paper |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
23,803
|
22,154
|
| Fair Value, available-for-sale investments |
23,803
|
22,154
|
| Level 2 | Commercial paper | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,991
|
|
| Level 2 | Commercial paper | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
$ 20,812
|
$ 22,154
|