Unsecured Convertible Senior Notes - 2023 Convertible Senior Notes (Details) $ / shares in Units, shares in Millions			12 Months Ended
	Aug. 14, 2020 USD ($) shares	Nov. 15, 2018 USD ($) $ / shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Adjustments to additional paid-in capital due to repurchase of the equity component			$ 22,073,000
Loss on early extinguishment of debt			13,374,000	$ 12,993,000
Principal amount			320,030,000
Proceeds from termination of capped call contracts			7,549,000
2023 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount		$ 210,000,000.0
Interest rate (as a percent)		6.25%
Net proceeds available for corporate use		$ 23,974,000
Conversion rate		0.0520183
Value used in calculation of conversion rate		$ 1,000
Conversion price | $ / shares		$ 19.22
Proceeds from 2026 debt issuance used to repurchase 2023 Notes	$ 125,600,000
Principal amount of debt repurchased	115,000,000.0
Fair value of the liability component	$ 103,600,000
Effective interest rate (as a percent)	9.90%
Adjustments to additional paid-in capital due to repurchase of the equity component	$ 22,000,000.0
Amount outstanding	90,200,000
Loss on early extinguishment of debt	13,400,000
Principal amount	$ 95,000,000.0		$ 95,000,000		$ 210,000,000
Number of underlying shares | shares	6.0
Proceeds from termination of capped call contracts	$ 7,500,000
Settlement loss upon termination of cap call contract	$ 800,000
Number of shares outstanding on the 2023 Capped Call | shares			4.9
2023 Convertible Senior Notes | Minimum
Debt Instrument [Line Items]
Conversion price | $ / shares		19.22
2023 Convertible Senior Notes | Maximum
Debt Instrument [Line Items]
Conversion price | $ / shares		$ 28.84