Long-Term Debt - Notes Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Mar. 31, 2016
Debt Disclosure [Abstract]
Principal amount of Notes	$ 325,000	$ 325,000	$ 325,000
Unamortized debt issuance costs	(1,898)	(2,965)
Total convertible notes payable	$ 323,102	$ 322,035

Face (par) amount of debt instrument at time of issuance.

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Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant