| Summary of Marketable Securities | The amortized cost and fair value of marketable securities as of the dates indicated below were as follows: 
|  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| As of December 31, 2019 (In thousands) | Amortized Cost |   | Gross Unrealized Gains |   | Gross Unrealized Losses |   | Fair Value |  
| Corporate debt securities | $ | 385,444 | 
 |   | $ | 623 | 
 |   | $ | (32 | ) |   | $ | 386,035 | 
 |  
| Money market funds and other | 435,933 | 
 |   | — | 
 |   | — | 
 |   | 435,933 | 
 |  
| Municipal securities | 9,212 | 
 |   | 9 | 
 |   | (3 | ) |   | 9,218 | 
 |  
| Sovereign securities | 6,005 | 
 |   | 8 | 
 |   | — | 
 |   | 6,013 | 
 |  
| U.S. Government agency securities | 94,739 | 
 |   | 50 | 
 |   | (13 | ) |   | 94,776 | 
 |  
| U.S. Treasury securities | 247,182 | 
 |   | 239 | 
 |   | (37 | ) |   | 247,384 | 
 |  
| Subtotal | 1,178,515 | 
 |   | 929 | 
 |   | (85 | ) |   | 1,179,359 | 
 |  
| 
Add: Time deposits(1)
 | 85,667 | 
 |   | — | 
 |   | — | 
 |   | 85,667 | 
 |  
| Less: Cash equivalents | 527,368 | 
 |   | — | 
 |   | — | 
 |   | 527,368 | 
 |  
| Marketable securities | $ | 736,814 | 
 |   | $ | 929 | 
 |   | $ | (85 | ) |   | $ | 737,658 | 
 | 
|  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| As of June 30, 2019 (In thousands) | AmortizedCost
 |   | GrossUnrealized
 Gains
 |   | GrossUnrealized
 Losses
 |   | FairValue
 |  
| Corporate debt securities | $ | 433,518 | 
 |   | $ | 141 | 
 |   | $ | (582 | ) |   | $ | 433,077 | 
 |  
| Money market funds and other | 352,708 | 
 |   | — | 
 |   | — | 
 |   | 352,708 | 
 |  
| Municipal securities | 1,910 | 
 |   | 3 | 
 |   | — | 
 |   | 1,913 | 
 |  
| Sovereign securities | 6,001 | 
 |   | 1 | 
 |   | (8 | ) |   | 5,994 | 
 |  
| U.S. Government agency securities | 159,454 | 
 |   | 5 | 
 |   | (241 | ) |   | 159,218 | 
 |  
| U.S. Treasury securities | 208,058 | 
 |   | 39 | 
 |   | (401 | ) |   | 207,696 | 
 |  
| Subtotal | 1,161,649 | 
 |   | 189 | 
 |   | (1,232 | ) |   | 1,160,606 | 
 |  
| 
Add: Time deposits(1)
 | 99,006 | 
 |   | — | 
 |   | — | 
 |   | 99,006 | 
 |  
| Less: Cash equivalents | 536,206 | 
 |   | 17 | 
 |   | (2 | ) |   | 536,221 | 
 |  
| Marketable securities | $ | 724,449 | 
 |   | $ | 172 | 
 |   | $ | (1,230 | ) |   | $ | 723,391 | 
 | ________________ (1)   Time deposits excluded from fair value measurements. | 
| Investments with Gross Unrealized Losses | The following table summarizes the fair value and gross unrealized losses of our investments that were in an unrealized loss position as of the date indicated below, $68.3 million of which were in a continuous loss position for 12 months or more: 
|  |  
|  |  |  |  |  |  |  |  |  
| As of December 31, 2019 (In thousands) | Fair Value |   | Gross  Unrealized  Losses |  
| Corporate debt securities | $ | 88,354 | 
 |   | $ | (32 | ) |  
| Municipal securities | 3,671 | 
 |   | (3 | ) |  
| U.S. Government agency securities | 37,246 | 
 |   | (13 | ) |  
| U.S Treasury securities | 87,526 | 
 |   | (37 | ) |  
| Total | $ | 216,797 | 
 |   | $ | (85 | ) | 
 
 
 
 | 
| Contractual Maturities of Securities | The contractual maturities of securities classified as available-for-sale, regardless of their classification on our Condensed Consolidated Balance Sheets, as of the date indicated below were as follows: 
|  |  
|  |  |  |  |  |  |  |  |  
| As of December 31, 2019 (In thousands) | Amortized Cost |   | Fair Value |  
| Due within one year | $ | 386,442 | 
 |   | $ | 386,617 | 
 |  
| Due after one year through three years | 350,372 | 
 |   | 351,041 | 
 |  
|   | $ | 736,814 | 
 |   | $ | 737,658 | 
 | 
 |