Summary of Significant Accounting Policies - Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment charges	$ 0.0	$ 0.0
Net book value of intangible assets	51.7	55.2
Indefinite-lived intangible assets (excluding goodwill)	34.1	34.1
Intangible assets, gross	44.6	44.6
Amortization expense from intangible assets	$ 3.4	$ 4.7	$ 5.0
Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets with defined useful lives, amortization period	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets with defined useful lives, amortization period	12 years