Investments - Schedule of Investments (Details) - USD ($)
$ in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
| Available-for-sale securities: |
|
|
| Amortized Cost |
$ 405,738
|
|
| Estimated Fair Value |
407,010
|
|
| Held-to-maturity securities: |
|
|
| Estimated Fair Value |
3,589
|
|
| Long-term Investments |
|
|
| Total long-term investments |
79,391
|
$ 80,744
|
| Total investments |
|
|
| Amortized Cost |
409,225
|
353,758
|
| Gross Unrealized Gains |
1,460
|
393
|
| Gross Unrealized Losses, Less than One Year |
(78)
|
(291)
|
| Gross Unrealized Losses, Greater than One Year |
(8)
|
(583)
|
| Estimated Fair Value |
410,599
|
353,277
|
| Short-term Investments |
|
|
| Amortized Cost |
329,862
|
272,835
|
| Gross Unrealized Gains |
1,358
|
257
|
| Gross Unrealized Losses, Less than One Year |
(11)
|
(81)
|
| Gross Unrealized Losses, Greater than One Year |
(1)
|
(478)
|
| Total short-term investments |
331,208
|
272,533
|
| Short-term investments |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
|
272,343
|
| Gross Unrealized Gains |
|
257
|
| Gross Unrealized Losses, Less than One Year |
|
(81)
|
| Gross Unrealized Losses, Greater than One Year |
|
(478)
|
| Estimated Fair Value |
|
272,041
|
| Short-term investments | U.S. government and agency debt securities |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
112,948
|
80,055
|
| Gross Unrealized Gains |
434
|
115
|
| Gross Unrealized Losses, Less than One Year |
(1)
|
(11)
|
| Gross Unrealized Losses, Greater than One Year |
(1)
|
(87)
|
| Estimated Fair Value |
113,380
|
80,072
|
| Short-term investments | Corporate debt securities |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
144,161
|
120,197
|
| Gross Unrealized Gains |
676
|
57
|
| Gross Unrealized Losses, Less than One Year |
|
(62)
|
| Gross Unrealized Losses, Greater than One Year |
|
(274)
|
| Estimated Fair Value |
144,837
|
119,918
|
| Held-to-maturity securities: |
|
|
| Amortized Cost |
|
492
|
| Estimated Fair Value |
|
492
|
| Short-term investments | International government agency debt securities |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
72,753
|
72,091
|
| Gross Unrealized Gains |
248
|
85
|
| Gross Unrealized Losses, Less than One Year |
(10)
|
(8)
|
| Gross Unrealized Losses, Greater than One Year |
|
(117)
|
| Estimated Fair Value |
72,991
|
72,051
|
| Long-term investments |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
75,876
|
77,436
|
| Gross Unrealized Losses, Less than One Year |
(67)
|
(210)
|
| Gross Unrealized Losses, Greater than One Year |
(7)
|
(105)
|
| Estimated Fair Value |
75,802
|
77,121
|
| Held-to-maturity securities: |
|
|
| Amortized Cost |
3,487
|
3,487
|
| Gross Unrealized Gains |
102
|
136
|
| Estimated Fair Value |
3,589
|
3,623
|
| Long-term Investments |
|
|
| Amortized Cost |
79,363
|
80,923
|
| Gross Unrealized Gains |
102
|
136
|
| Gross Unrealized Losses, Less than One Year |
(67)
|
(210)
|
| Gross Unrealized Losses, Greater than One Year |
(7)
|
(105)
|
| Total long-term investments |
79,391
|
80,744
|
| Long-term investments | Certificates of deposit |
|
|
| Held-to-maturity securities: |
|
|
| Amortized Cost |
1,820
|
1,820
|
| Estimated Fair Value |
1,820
|
1,820
|
| Long-term investments | U.S. government and agency debt securities |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
4,000
|
18,474
|
| Gross Unrealized Losses, Less than One Year |
(4)
|
(21)
|
| Gross Unrealized Losses, Greater than One Year |
|
(12)
|
| Estimated Fair Value |
3,996
|
18,441
|
| Long-term investments | Corporate debt securities |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
51,070
|
53,505
|
| Gross Unrealized Losses, Less than One Year |
(45)
|
(185)
|
| Gross Unrealized Losses, Greater than One Year |
(7)
|
(93)
|
| Estimated Fair Value |
51,018
|
53,227
|
| Long-term investments | International government agency debt securities |
|
|
| Available-for-sale securities: |
|
|
| Amortized Cost |
20,806
|
5,457
|
| Gross Unrealized Losses, Less than One Year |
(18)
|
(4)
|
| Estimated Fair Value |
20,788
|
5,453
|
| Long-term investments | Fixed Term Deposit Account |
|
|
| Held-to-maturity securities: |
|
|
| Amortized Cost |
1,667
|
1,667
|
| Gross Unrealized Gains |
102
|
136
|
| Estimated Fair Value |
$ 1,769
|
$ 1,803
|