Short-Term Investments (Details) - USD ($) $ in Thousands |
Jun. 30, 2021 |
Dec. 31, 2020 |
---|---|---|
Debt Securities, Available-for-sale [Line Items] | ||
Amortized Cost | $ 120,211 | $ 29,528 |
Gross Unrealized Losses | (3) | |
Estimated Fair Value | 120,208 | 29,528 |
Municipal bonds and notes | ||
Debt Securities, Available-for-sale [Line Items] | ||
Amortized Cost | 2,027 | 28,998 |
Gross Unrealized Losses | (1) | |
Estimated Fair Value | 2,026 | 28,998 |
Zero coupon bonds | ||
Debt Securities, Available-for-sale [Line Items] | ||
Amortized Cost | 117,654 | |
Gross Unrealized Losses | (2) | |
Estimated Fair Value | 117,652 | |
Certificates of deposit | ||
Debt Securities, Available-for-sale [Line Items] | ||
Amortized Cost | 530 | 530 |
Estimated Fair Value | $ 530 | $ 530 |