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Income Taxes - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017 | Dec. 31, 2020 | Dec. 31, 2019
Schedule Of Income Taxes [Line Items] |  |  |  |
Income tax expense due to re-measurement of deferred tax assets and liabilities as result of changes in federal tax rate |  | $ 13,400 |  |
Income tax benefit | $ 3,000 |  |  |
Valuation allowance related to gross deferred tax assets |  |  | $ 5,489 | $ 5,134
Deferred tax assets, net operating loss carry forwards |  |  | 54,900 |
PENNSYLVANIA |  |  |  |
Schedule Of Income Taxes [Line Items] |  |  |  |
Valuation allowance related to gross deferred tax assets |  |  | $ 5,500 | $ 5,100

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