Short-Term and Long-Term Investments Schedule of Investments in an Unrealized Loss Position (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018 |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | $ 164,476 | $ 202,019 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (28) | (380) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 145,514 | 143,370 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (309) | (525) |
Debt Securities, Available-for-sale, Unrealized Loss Position | 309,990 | 345,389 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | (337) | (905) |
Short-term investments | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 161,488 | 180,775 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (27) | (274) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 145,514 | 143,370 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (309) | (525) |
Debt Securities, Available-for-sale, Unrealized Loss Position | 307,002 | 324,145 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | (336) | (799) |
Short-term investments | U.S. treasury securities | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 80,890 | 89,320 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (11) | (143) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 99,972 | 79,472 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (222) | (314) |
Debt Securities, Available-for-sale, Unrealized Loss Position | 180,862 | 168,792 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | (233) | (457) |
Short-term investments | U.S. agency securities | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 2,059 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 8,560 | 18,515 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (16) | (61) |
Debt Securities, Available-for-sale, Unrealized Loss Position | 10,619 | 18,515 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | (16) | (61) |
Short-term investments | Corporate bonds | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 78,539 | 91,455 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (16) | (131) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 36,982 | 45,383 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (71) | (150) |
Debt Securities, Available-for-sale, Unrealized Loss Position | 115,521 | 136,838 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | (87) | (281) |
Long-term investments | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 2,988 | 21,244 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (1) | (106) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Unrealized Loss Position | 2,988 | 21,244 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | (1) | (106) |
Long-term investments | U.S. treasury securities | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | | 9,855 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | | (50) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | | 0 |
Debt Securities, Available-for-sale, Unrealized Loss Position | | 9,855 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | | (50) |
Long-term investments | Corporate bonds | | |
Schedule of Short-Term and Long-Term Investments | | |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 2,988 | 11,389 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (1) | (56) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 0 | 0 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0 | 0 |
Debt Securities, Available-for-sale, Unrealized Loss Position | 2,988 | 11,389 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | $ (1) | $ (56) |