Financial Instruments (Fair Value Measurements) (Details) - Measured on a recurring basis - USD ($)
$ in Thousands |
Mar. 31, 2016 |
Dec. 31, 2015 |
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
$ 47,724
|
$ 81,068
|
| Unrealized Gains, available-for-sale securities |
16
|
2
|
| Unrealized Losses, available-for-sale securities |
(3)
|
(63)
|
| Fair Value, assets |
47,737
|
81,007
|
| Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
17,004
|
29,530
|
| Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
24,002
|
37,761
|
| Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
6,732
|
13,716
|
| Cash |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
6,342
|
7,593
|
| Cash | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
6,342
|
7,593
|
| Level 1 |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, assets |
11,660
|
22,935
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
|
(2)
|
| Fair Value, assets |
11,661
|
22,933
|
| Level 1 | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
10,662
|
21,937
|
| Level 1 | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
999
|
|
| Level 1 | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
996
|
| Level 1 | Money market funds |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
10,662
|
21,937
|
| Level 1 | Money market funds | Cash and Cash Equivalents |
|
|
| Fair Value Measurements |
|
|
| Fair value, cash and cash equivalents |
10,662
|
21,937
|
| Level 1 | U.S. government notes |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
998
|
998
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
|
(2)
|
| Fair Value, available-for-sale investments |
999
|
996
|
| Level 1 | U.S. government notes | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
999
|
|
| Level 1 | U.S. government notes | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
996
|
| Level 2 |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
|
50,540
|
| Unrealized Gains, available-for-sale securities |
|
2
|
| Unrealized Losses, available-for-sale securities |
|
(61)
|
| Fair Value, available-for-sale investments |
|
50,481
|
| Level 2 | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
37,761
|
| Level 2 | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
12,720
|
| Level 2 | Available-for-sale investments |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
29,722
|
|
| Unrealized Gains, available-for-sale securities |
15
|
|
| Unrealized Losses, available-for-sale securities |
(3)
|
|
| Fair Value, available-for-sale investments |
29,734
|
|
| Level 2 | Available-for-sale investments | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
23,003
|
|
| Level 2 | Available-for-sale investments | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
6,732
|
|
| Level 2 | Asset-backed securities |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
5,334
|
6,739
|
| Unrealized Gains, available-for-sale securities |
3
|
|
| Unrealized Losses, available-for-sale securities |
|
(9)
|
| Fair Value, available-for-sale investments |
5,337
|
6,730
|
| Level 2 | Asset-backed securities | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
28
|
|
| Level 2 | Asset-backed securities | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
5,308
|
6,730
|
| Level 2 | Corporate bonds |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
22,887
|
39,195
|
| Unrealized Gains, available-for-sale securities |
11
|
2
|
| Unrealized Losses, available-for-sale securities |
(3)
|
(51)
|
| Fair Value, available-for-sale investments |
22,895
|
39,146
|
| Level 2 | Corporate bonds | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
21,473
|
33,156
|
| Level 2 | Corporate bonds | Long-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
1,424
|
5,990
|
| Level 2 | Commercial paper |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
|
1,100
|
| Fair Value, available-for-sale investments |
|
1,100
|
| Level 2 | Commercial paper | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
|
1,100
|
| Level 2 | U.S. agency securities |
|
|
| Fair Value Measurements |
|
|
| Adjusted Cost, available-for-sale securities |
1,501
|
3,506
|
| Unrealized Gains, available-for-sale securities |
1
|
|
| Unrealized Losses, available-for-sale securities |
|
(1)
|
| Fair Value, available-for-sale investments |
1,502
|
3,505
|
| Level 2 | U.S. agency securities | Short-term investments |
|
|
| Fair Value Measurements |
|
|
| Fair Value, available-for-sale investments |
$ 1,502
|
$ 3,505
|