Long-term Debt - 2025 Notes (Details) $ / shares in Units, shares in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018 USD ($) shares $ / shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 24, 2018 USD ($)	Oct. 22, 2018 USD ($)
Debt Instrument [Line Items]
Carrying amount		$ 293,667,000	$ 221,041,000
Senior Convertible Notes Due 2025
Debt Instrument [Line Items]
Debt issuance costs	$ 5,900,000
Senior Notes | Senior Convertible Notes Due 2025
Debt Instrument [Line Items]
Face amount	$ 172,500,000	172,500,000	172,500,000	$ 22,500,000	$ 150,000,000.0
Interest rate	1.50%
Proceeds from issuance of debt	$ 166,600,000
Debt issuance costs	3,400,000
Interest expense		2,600,000	500,000
Debt conversion denominator shares per principal amount	$ 1,000
Conversion price (in dollars per share) | $ / shares	$ 33.43
Initial conversion amount (in shares) | shares	5.2
Carrying amount	$ 100,700,000
Non-cash amortization of debt discount and debt issuance costs		$ 8,500,000	$ 1,500,000
Repurchase covenant, repurchase price due to fundamental change as percentage of principal amount	100.00%
Repurchase covenant, sale price as a percentage of conversion price	130.00%
Repurchase covenant, trading days, minimum	20 days
Repurchase covenant, consecutive trading days, minimum	30 days
Repurchase covenant, repurchase price due to change in sale price as percentage of conversion price	100.00%
Senior Notes | Senior Convertible Notes Due 2025 | Common Stock
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 71,800,000
Debt issuance costs	$ 2,500,000
Senior Notes | Senior Convertible Notes Due 2025 | Class A Common Stock | Common Stock
Debt Instrument [Line Items]
Initial conversion rate per $ 1000 principal amount	0.0299135