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Intangible Assets and Deferred Charges - Schedule of Intangible Assets (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]    
Intangible assets, gross $ 30,866 $ 30,866
Accumulated amortization of intangible assets (21,481) (19,440)
Intangible assets, net $ 9,385 $ 11,426