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Marketable Securities - Additional Information (Details) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items] |  |  |
Unrealized loss position for a period longer than twelve months | $ 0 |  |
Allowance for credit losses | 0 |  |
Impairment charges | 0 | $ 0 |
Marketable securities, due within one year | 26,842,000 |  | $ 34,874,000
Proceeds from maturities of available-for-sale securities | 9,905,000 | 12,910,000 |
Proceeds from sale of marketable securities | 0 | $ 0 |
Variable rate demand notes |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Marketable securities, due within one year | $ 5,600,000 |  |
Variable rate demand notes | Minimum |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Contractual maturities (in years) | 17 years |  |
Settlement basis period (in days) | 1 day |  |
Effective maturity period (in days) | 1 day |  |
Variable rate demand notes | Maximum |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Contractual maturities (in years) | 26 years |  |
Settlement basis period (in days) | 7 days |  |
Effective maturity period (in days) | 7 days |  |

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