Fair Value Measurements - Carrying Amounts and Estimated Fair Values by Input Level (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Jan. 19, 2017
Financial assets:
Equity securities	$ 18.7	$ 40.5
Financial liabilities:
Interest rate	5.625%
Senior notes | 5.625% Notes
Financial liabilities:
Interest rate	5.625%	5.625%	5.625%
Carrying Amount | Recurring
Financial assets:
Cash and cash equivalents	$ 730.7	$ 437.4
Equity securities	18.7	40.5
Held-to-maturity securities	6.6	6.7
Promissory notes	15.1	15.1
Financial liabilities:
Other liabilities	18.1	20.3
Carrying Amount | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	2,416.7	1,896.5
Carrying Amount | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	399.5	399.4
Carrying Amount | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	80.8	89.2
Fair Value | Recurring
Financial assets:
Cash and cash equivalents	730.7	437.4
Equity securities	18.7	40.5
Held-to-maturity securities	6.6	6.7
Promissory notes	15.2	15.1
Financial liabilities:
Other liabilities	18.1	20.3
Fair Value | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	2,120.0	1,930.6
Fair Value | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	296.0	426.0
Fair Value | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	81.1	89.7
Level 1 | Recurring
Financial assets:
Cash and cash equivalents	730.7	437.4
Equity securities	0.0	0.0
Held-to-maturity securities	0.0	0.0
Promissory notes	0.0	0.0
Financial liabilities:
Other liabilities	0.0	0.0
Level 1 | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	2,120.0	1,930.6
Level 1 | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	296.0	426.0
Level 1 | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	0.0	0.0
Level 2 | Recurring
Financial assets:
Cash and cash equivalents	0.0	0.0
Equity securities	18.7	40.5
Held-to-maturity securities	6.6	6.7
Promissory notes	15.2	15.1
Financial liabilities:
Other liabilities	2.8	2.8
Level 2 | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	0.0	0.0
Level 2 | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	0.0	0.0
Level 2 | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	81.1	89.7
Level 3 | Recurring
Financial assets:
Cash and cash equivalents	0.0	0.0
Equity securities	0.0	0.0
Held-to-maturity securities	0.0	0.0
Promissory notes	0.0	0.0
Financial liabilities:
Other liabilities	15.3	17.5
Level 3 | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	0.0	0.0
Level 3 | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	0.0	0.0
Level 3 | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	$ 0.0	$ 0.0