Long-term Debt - 2.25% Convertible Senior Notes (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) d $ / shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / shares	Dec. 14, 2016 USD ($)
Debt Instrument [Line Items]
Current portion of long-term debt	$ 297,700,000		$ 297,700,000		$ 284,700,000
Carrying value	$ 615,000,000.0		$ 615,000,000.0		628,100,000
Share price (in USD per share) | $ / shares	$ 39.89		$ 39.89
Interest expense components for 2 1/4% Notes
Interest expense-contractual interest	$ 1,700,000	$ 1,700,000	$ 5,100,000	$ 5,100,000
Interest expense-amortization of debt discount	2,000,000.0	1,900,000	5,900,000	5,600,000
Interest expense-amortization of deferred financing costs	200,000	$ 200,000	500,000	$ 500,000
2 1/4% Notes
Debt Instrument [Line Items]
Carrying value	300,000,000.0		$ 300,000,000.0		300,000,000.0
Convertible Debt | 2 1/4% Notes
Debt Instrument [Line Items]
Principal amount						$ 300,000,000.0
Debt convertible trigger stock price (in USD per share) | $ / shares			$ 33.80
Debt convertible threshold trading days | d			20
Debt convertible threshold consecutive trading days | d			30
Current portion of long-term debt	269,400,000		$ 269,400,000
Convertible debt threshold percentage of stock price trigger			130.00%
Carrying value	269,400,000		$ 269,400,000		263,000,000.0
Unamortized discount and deferred financing costs	30,600,000		30,600,000		37,000,000.0
Principal amount	300,000,000.0		300,000,000.0		300,000,000.0
Carrying amount of equity component, net of equity issuance costs	$ 54,500,000		$ 54,500,000		$ 54,500,000
Remaining amortization period (years)			3 years 3 months		4 years
Effective interest rate (as a percent)	5.80%		5.80%		5.80%
Conversion rate (shares of common stock per $1,000 principal amount)			0.0384615		0.0384615
Conversion price (in USD per share) | $ / shares	$ 26.00		$ 26.00		$ 26.00
Debt Component of Convertible Debt | 2 1/4% Notes
Debt Instrument [Line Items]
If-converted value in excess of principal			$ 160,300,000