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 |