Financial Instruments (Details) - Measured on a recurring basis - USD ($)
$ in Thousands |
Mar. 31, 2017 |
Dec. 31, 2016 |
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
$ 55,326
|
$ 61,806
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
(20)
|
(15)
|
| Fair Value, assets |
55,307
|
61,791
|
| Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
28,215
|
34,813
|
| Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
23,988
|
22,970
|
| Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
3,104
|
4,008
|
| Cash |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
18,044
|
24,708
|
| Cash | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
18,044
|
24,708
|
| Level 1 |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
15,275
|
12,106
|
| Unrealized Losses, available-for-sale securities |
(7)
|
(1)
|
| Fair Value, assets |
15,268
|
12,105
|
| Level 1 | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
10,171
|
10,105
|
| Level 1 | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
3,994
|
2,000
|
| Level 1 | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
1,103
|
|
| Level 1 | Money market funds |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
10,171
|
10,105
|
| Level 1 | Money market funds | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
10,171
|
10,105
|
| Level 1 | U.S. government notes |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
5,104
|
2,001
|
| Unrealized Losses, available-for-sale securities |
(7)
|
(1)
|
| Fair Value, available-for-sale investments |
5,097
|
2,000
|
| Level 1 | U.S. government notes | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
3,994
|
2
|
| Level 1 | U.S. government notes | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
1,103
|
|
| Level 2 | Available-for-sale investments |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
22,007
|
24,992
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
(13)
|
(14)
|
| Fair Value, available-for-sale investments |
21,995
|
24,978
|
| Level 2 | Available-for-sale investments | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
19,994
|
20,970
|
| Level 2 | Available-for-sale investments | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,001
|
4,008
|
| Level 2 | Asset-backed securities |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
2,003
|
4,008
|
| Unrealized Losses, available-for-sale securities |
(2)
|
|
| Fair Value, available-for-sale investments |
2,001
|
4,008
|
| Level 2 | Asset-backed securities | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
2,001
|
4,008
|
| Level 2 | Corporate bonds |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
9,541
|
13,902
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
(11)
|
(14)
|
| Fair Value, available-for-sale investments |
9,531
|
13,888
|
| Level 2 | Corporate bonds | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
9,531
|
13,888
|
| Level 2 | Commercial paper |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
10,463
|
7,082
|
| Fair Value, available-for-sale investments |
10,463
|
7,082
|
| Level 2 | Commercial paper | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
$ 10,463
|
$ 7,082
|