Summary of Significant Accounting Policies - Net Loss per Share (Details) - $ / shares	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Stock appreciation rights
Net loss per share:
Antidilutive securities excluded (in shares)	4,911,656	6,623,466
Convertible Debt Securities
Net loss per share:
Converted (in shares)	2,385,800
Conversion price (in usd per share)	$ 136.20

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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-Name Accounting Standards Codification
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