Inventory Financing Agreements - Supply and Offtake Agreements (Details) - Supply and Offtake Agreements $ in Millions	Feb. 01, 2020 USD ($) settlement_payment	Jun. 27, 2018 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 01, 2018 USD ($)	Jun. 01, 2015 USD ($)
Supply Commitment [Line Items]
Amount of deferred payment arrangement		$ 165.0
Percentage of receivables and inventory for deferred payment arrangement		85.00%
Deferral arrangement fee						$ 1.3
Capacity of deferred payment arrangement			$ 102.0	$ 80.1
Outstanding amount of deferred payment arrangement			96.2	78.6
Fee agreement receivable (payable)	$ 0.8		$ 0.2	$ 0.5	$ 2.2
Number of settlement payments | settlement_payment	15