Summary of Significant Accounting Policies - Concentration Risk (Details)	12 Months Ended
Dec. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($) item
Concentrations of risk
Deferred revenue	$ 37,300,000	$ 92,600,000
Accrued interest	800,000	1,400,000
Impairment loss or recoveries	0	0
Amounts on deposit in excess of federally insured limits approximately	$ 143,200,000	$ 163,300,000
Minimum
Concentrations of risk
Collection period	30 days
Maximum
Concentrations of risk
Collection period	60 days
Accounts receivable \| Customers \| Major Customers
Concentrations of risk
Concentration risk percentage	84.00%	88.00%
Accounts receivable \| Service providers
Concentrations of risk
Number of service providers \| item	2	2
Payables \| Service providers
Concentrations of risk
Number of service providers \| item	4	1
Number of critical suppliers \| item	4
Payables \| Service providers \| Major Vendors
Concentrations of risk
Concentration risk percentage	64.00%	49.00%

The amount of cash as of the balance sheet date that is not insured by the Federal Deposit Insurance Corporation.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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Carrying amount as of the balance sheet date of current interest earned but not received. Also called accrued interest or accrued interest receivable. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

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Represents the duration of time typical for accounts receivable collection.

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Amount of impairment loss or recovery related to marketable securities.

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Represents the number of critical suppliers.

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Represents the number of service providers.

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