Long-term Debt - 2.25% Convertible Senior Notes (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) d $ / shares	Jun. 30, 2019 USD ($)	Dec. 31, 2018	Dec. 31, 2019 USD ($) $ / shares	Dec. 14, 2016 USD ($)
Debt Instrument [Line Items]
Current portion of long-term debt	$ 293,200,000		$ 293,200,000			$ 284,700,000
Carrying value	$ 619,400,000		$ 619,400,000			628,100,000
Share price (in USD per share) | $ / shares	$ 39.64		$ 39.64
Interest expense components for 2 1/4% Notes
Interest expense-contractual interest	$ 1,700,000	$ 1,700,000	$ 3,400,000	$ 3,400,000
Interest expense-amortization of debt discount	2,000,000.0	1,900,000	3,900,000	3,700,000
Interest expense-amortization of deferred financing costs	100,000	$ 100,000	300,000	$ 300,000
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	$ 267,200,000		$ 267,200,000
Convertible debt threshold percentage of stock price trigger			130.00%
Effective interest rate (as a percent)	5.80%		5.80%			5.80%
Carrying value	$ 267,200,000		$ 267,200,000			$ 263,000,000.0
Unamortized discount and deferred financing costs	32,800,000		32,800,000			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 6 months		4 years
Conversion rate (shares of common stock per $1,000 principal amount)			38.4615		38.4615
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			$ 157,400,000