Convertible Notes - Narrative (Details)				12 Months Ended
	Apr. 06, 2018 USD ($)	Apr. 04, 2018 USD ($) day	Mar. 27, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Over-allotment option, term			13 days
Over-allotment option			$ 22,500,000
Additional proceeds		$ 21,500,000
Conversion ratio			0.0323428
Outstanding principal				$ 171,500,000	$ 171,500,000
Unamortized debt issuance				2,415,000	2,996,000
Stock price conversion threshold, percentage		130.00%
Consecutive trading days | day		20
Threshold trading days		30
Trading price threshold, percentage		98.00%
Repurchase principal balance, percent	100.00%
Interest expense				4,300,000	3,300,000
Amortization of debt issuance costs				600,000	400,000
Amortization of the debt discount				$ 9,400,000	$ 6,500,000
Net proceeds from notes to fund Prepaid Forward	$ 45,100,000
Aggregate number of shares | shares				1,858,500
Unsecured Obligations | 2.50% Convertible Notes due 2023
Debt Instrument [Line Items]
Aggregate principal amount		$ 171,500,000	$ 150,000,000
Interest rate			2.50%
Proceeds from issuance of notes		171,500,000
Conversion multiple		1,000
Initial conversion price (usd per share) | $ / shares			$ 30.92
Outstanding principal		116,600,000
Equity component		(54,900,000)
Unamortized debt issuance		$ 5,000,000.0
Contractual term	5 years
Effective interest rate		11.52%
Unsecured Obligations | 2.50% Convertible Notes due 2023 | Long-Term Debt
Debt Instrument [Line Items]
Unamortized debt issuance		$ 3,400,000
Unsecured Obligations | 2.50% Convertible Notes due 2023 | Contributed Capital
Debt Instrument [Line Items]
Unamortized debt issuance		$ 1,600,000