Restructuring Charges, Net of Reversals and Impairment, and Related Charges (Narratives) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	Dec. 31, 2020
Restructuring Cost And Reserve [Line Items]
Restructuring charges, net of reversals and impairment	$ 0.7		$ 1.7
Facility related charges	0.3		0.6
Severance and benefits charges	$ 0.4		$ 1.1
Reduction-in-force
Restructuring Cost And Reserve [Line Items]
Reduction in force or severance and benefits						$ 9.2
Reduction-in-force | Scenario Forecast
Restructuring Cost And Reserve [Line Items]
Reduction in force or severance and benefits					$ 0.8
Prior year Reduction-in-force plans
Restructuring Cost And Reserve [Line Items]
Restructuring charges, net of reversals and impairment		$ 6.6		$ 12.8
Severance and benefits charges		2.7		4.9
Prior year Reduction-in-force plans | Non-Cancelable Lease Payments
Restructuring Cost And Reserve [Line Items]
Charges for impairment of right-of-use assets		$ 3.9		$ 7.9