Amount of amortization expense attributable to debt issuance costs.

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Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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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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Amount of unamortized debt discount (premium) and debt issuance costs.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Long-term Debt - Convertible Senior Notes Carrying Value (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Oct. 31, 2018	Oct. 24, 2018	Oct. 22, 2018	Dec. 31, 2016
Debt Disclosure [Abstract]
Amortization of deferred financing costs	$ 3,009,000	$ 2,279,000
Senior Notes \| Senior Convertible Notes Due 2025
Debt Instrument [Line Items]
Carrying value	109,393,000		$ 107,169,000
Unamortized debt discount and issuance costs allocated to debt	63,107,000		65,331,000
Principal amount	$ 172,500,000		$ 172,500,000	$ 172,500,000	$ 22,500,000	$ 150,000,000.0
Remaining amortization period (years)	5 years 6 months		5 years 9 months 18 days
Senior Notes \| Senior Convertible Notes Due 2025 \| Level 2
Debt Instrument [Line Items]
Fair value	$ 109,800,000		$ 122,000,000.0
Senior Notes \| Convertible Senior Notes due 2021
Debt Disclosure [Abstract]
Amortization of deferred financing costs	200,000	$ 200,000
Debt Instrument [Line Items]
Carrying value	123,467,000		123,237,000
Unamortized debt discount and issuance costs allocated to debt	1,533,000		1,763,000
Principal amount	$ 125,000,000		$ 125,000,000				$ 125,000,000.0
Remaining amortization period (years)	1 year 8 months 12 days		1 year 10 months 24 days
Senior Notes \| Convertible Senior Notes due 2021 \| Level 2
Debt Instrument [Line Items]
Fair value	$ 103,200,000		$ 111,300,000