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Revenue Recognition - Contract Balances (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Contract with Customer, Asset and Liability, Rollforward [Roll Forward]    
Balance at beginning of period $ 357 $ 185
Cash received, excluding amounts recognized as revenue 228 777
Amounts recognized as revenue (347) (605)
Balance at end of period $ 238 $ 357