Financial Instruments (Details) - Measured on a recurring basis - USD ($)
$ in Thousands |
Jun. 30, 2017 |
Dec. 31, 2016 |
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
$ 64,797
|
$ 61,806
|
| Unrealized Losses, available-for-sale securities |
(18)
|
(15)
|
| Fair Value, assets |
64,779
|
61,791
|
| Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
30,063
|
34,813
|
| Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
32,707
|
22,970
|
| Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,009
|
4,008
|
| Cash |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
22,467
|
24,708
|
| Cash | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
22,467
|
24,708
|
| Level 1 |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
10,197
|
12,106
|
| Unrealized Losses, available-for-sale securities |
(9)
|
(1)
|
| Fair Value, assets |
10,188
|
12,105
|
| Level 1 | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
5,098
|
10,105
|
| Level 1 | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
5,090
|
2,000
|
| Level 1 | Money market funds |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
5,098
|
10,105
|
| Level 1 | Money market funds | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
5,098
|
10,105
|
| Level 1 | U.S. government notes |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
5,099
|
2,001
|
| Unrealized Losses, available-for-sale securities |
(9)
|
(1)
|
| Fair Value, available-for-sale investments |
5,090
|
2,000
|
| Level 1 | U.S. government notes | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
5,090
|
2
|
| Level 2 | Available-for-sale investments |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
32,133
|
24,992
|
| Unrealized Losses, available-for-sale securities |
(9)
|
(14)
|
| Fair Value, available-for-sale investments |
32,124
|
24,978
|
| Level 2 | Available-for-sale investments | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,498
|
|
| Level 2 | Available-for-sale investments | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
27,617
|
20,970
|
| Level 2 | Available-for-sale investments | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,009
|
4,008
|
| Level 2 | Asset-backed securities |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
1,002
|
4,008
|
| Unrealized Losses, available-for-sale securities |
(1)
|
|
| Fair Value, available-for-sale investments |
1,001
|
4,008
|
| Level 2 | Asset-backed securities | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
1,001
|
4,008
|
| Level 2 | Corporate bonds |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
13,818
|
13,902
|
| Unrealized Losses, available-for-sale securities |
(8)
|
(14)
|
| Fair Value, available-for-sale investments |
13,810
|
13,888
|
| Level 2 | Corporate bonds | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
12,802
|
13,888
|
| Level 2 | Corporate bonds | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
1,008
|
|
| Level 2 | Commercial paper |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
14,815
|
7,082
|
| Fair Value, available-for-sale investments |
14,815
|
7,082
|
| Level 2 | Commercial paper | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
14,815
|
$ 7,082
|
| Level 2 | U.S. agency securities |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
2,498
|
|
| Fair Value, available-for-sale investments |
2,498
|
|
| Level 2 | U.S. agency securities | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
$ 2,498
|
|