Financial Instruments and Fair Value Measurements - Fair Values of Financial Instruments Not Measured at Fair Value in Consolidated Balance Sheets (Details) - 5.50% convertible senior notes due 2021 - Senior Notes - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Aug. 06, 2019	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of long-term debt	$ 82.7	$ 80.0	$ 84.2
Interest rate	5.50%			5.50%
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long-term debt	$ 100.9	$ 115.8