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Unsecured Convertible Senior Notes - 2026 Convertible Senior Notes (Details) $ / shares in Units, shares in Millions	2 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) D $ / shares shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Aggregate principal amount outstanding		$ 320,030,000
Repurchase of 2023 Notes		(125,638,000)
Termination of the 2023 Capped Call contracts related to debt repurchased		7,549,000
Issuance costs		(6,785,000)	$ (6,800,000)
2026 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount	$ 225,000,000.0
Interest rate (as a percent)	5.25%
Aggregate principal amount outstanding		$ 225,030,000
2026 Notes principal amount issued	$ 225,030,000
Repurchase of 2023 Notes	(125,638,000)
Purchase of 2026 Capped Call	(23,223,000)
Termination of the 2023 Capped Call contracts related to debt repurchased	7,549,000
Issuance costs	(6,785,000)
Net proceeds available for corporate use	$ 76,933,000
Conversion rate	0.0540906
Value used in calculation of conversion rate	$ 1,000
Conversion price | $ / shares	$ 18.4875
Shares upon conversion | shares	12.2
Capped Call Transactions, Threshold Trading Day Period	50 days
Number of shares outstanding on the 2026 Capped Call | shares		12.2
Fair value of equity component	$ 23,200,000
Effective interest rate (as a percent)	12.50%
2026 Convertible Senior Notes | Debt Conversion, After September 30, 2020
Debt Instrument [Line Items]
Stock price trigger (as a percent)	130.00%
Trading days, number | D	20
Consecutive trading days, period | D	30
Consecutive business days, period	5 days
Consecutive trading-day period	5 days
Maximum product of the closing sale price of shares of the Company's common stock and the applicable conversion rate for such trading day (as a percent)	98.00%
2026 Convertible Senior Notes | Debt Conversion, On Or After August 15, 2023
Debt Instrument [Line Items]
Stock price trigger (as a percent)	130.00%
Trading days, number | D	20
Consecutive trading days, period | D	30
2026 Convertible Senior Notes | Minimum
Debt Instrument [Line Items]
Conversion price | $ / shares	$ 18.49
2026 Convertible Senior Notes | Maximum
Debt Instrument [Line Items]
Conversion price | $ / shares	$ 26.10

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