Financial Instruments (Fair Value Measurements) (Details) - Measured on a recurring basis - USD ($) $ in Thousands | Jun. 30, 2016 | Dec. 31, 2015 |
Fair Value Measurements | | |
Adjusted Cost, assets | $ 48,588 | $ 81,068 |
Unrealized Gains, available-for-sale securities | 9 | 2 |
Unrealized Losses, available-for-sale securities | | (63) |
Fair Value, assets | 48,597 | 81,007 |
Cash and Cash Equivalents | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 22,807 | 29,530 |
Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 20,780 | 37,761 |
Long-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 5,010 | 13,716 |
Cash | | |
Fair Value Measurements | | |
Fair value, cash and cash equivalents | 11,653 | 7,593 |
Cash | Cash and Cash Equivalents | | |
Fair Value Measurements | | |
Fair value, cash and cash equivalents | 11,653 | 7,593 |
Level 1 | | |
Fair Value Measurements | | |
Adjusted Cost, assets | 11,155 | 22,935 |
Unrealized Gains, available-for-sale securities | 1 | |
Unrealized Losses, available-for-sale securities | | (2) |
Fair Value, assets | 11,156 | 22,933 |
Level 1 | Cash and Cash Equivalents | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 10,156 | 21,937 |
Level 1 | Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 1,000 | |
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 | 10,156 | 21,937 |
Level 1 | Money market funds | Cash and Cash Equivalents | | |
Fair Value Measurements | | |
Fair value, cash and cash equivalents | 10,156 | 21,937 |
Level 1 | U.S. government notes | | |
Fair Value Measurements | | |
Adjusted Cost, available-for-sale securities | 999 | 998 |
Unrealized Gains, available-for-sale securities | 1 | |
Unrealized Losses, available-for-sale securities | | (2) |
Fair Value, available-for-sale investments | 1,000 | 996 |
Level 1 | U.S. government notes | Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 1,000 | |
Level 1 | U.S. government notes | Long-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | | 996 |
Level 2 | Available-for-sale investments | | |
Fair Value Measurements | | |
Adjusted Cost, available-for-sale securities | 25,780 | 50,540 |
Unrealized Gains, available-for-sale securities | 8 | 2 |
Unrealized Losses, available-for-sale securities | | (61) |
Fair Value, available-for-sale investments | 25,788 | 50,481 |
Level 2 | Available-for-sale investments | Cash and Cash Equivalents | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 998 | |
Level 2 | Available-for-sale investments | Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 19,780 | 37,761 |
Level 2 | Available-for-sale investments | Long-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 5,010 | 12,720 |
Level 2 | Asset-backed securities | | |
Fair Value Measurements | | |
Adjusted Cost, available-for-sale securities | 5,007 | 6,739 |
Unrealized Gains, available-for-sale securities | 3 | |
Unrealized Losses, available-for-sale securities | | (9) |
Fair Value, available-for-sale investments | 5,010 | 6,730 |
Level 2 | Asset-backed securities | Long-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 5,010 | 6,730 |
Level 2 | Corporate bonds | | |
Fair Value Measurements | | |
Adjusted Cost, available-for-sale securities | 17,777 | 39,195 |
Unrealized Gains, available-for-sale securities | 5 | 2 |
Unrealized Losses, available-for-sale securities | | (51) |
Fair Value, available-for-sale investments | 17,782 | 39,146 |
Level 2 | Corporate bonds | Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 17,782 | 33,156 |
Level 2 | Corporate bonds | Long-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | | 5,990 |
Level 2 | Commercial paper | | |
Fair Value Measurements | | |
Adjusted Cost, available-for-sale securities | 1,995 | 1,100 |
Fair Value, available-for-sale investments | 1,995 | 1,100 |
Level 2 | Commercial paper | Cash and Cash Equivalents | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 998 | |
Level 2 | Commercial paper | Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | 997 | 1,100 |
Level 2 | U.S. agency securities | | |
Fair Value Measurements | | |
Adjusted Cost, available-for-sale securities | 1,001 | 3,506 |
Unrealized Losses, available-for-sale securities | | (1) |
Fair Value, available-for-sale investments | 1,001 | 3,505 |
Level 2 | U.S. agency securities | Short-term investments | | |
Fair Value Measurements | | |
Fair Value, available-for-sale investments | $ 1,001 | $ 3,505 |