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Commitments and Contingencies - Purchase Obligations Narrative (Details) - Materials [Member]
$ in Thousands
Dec. 31, 2019
USD ($)
Recorded Unconditional Purchase Obligation [Line Items]  
Recorded unconditional purchase obligation 2020 $ 6,386
Recorded unconditional purchase obligation 2021 7,543
Recorded unconditional purchase obligation 2022 7,543
Recorded unconditional purchase obligation 2019 $ 7,807