Fair Value Measurements - Carrying Amounts and Estimated Fair Values by Input Level (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Jan. 19, 2017
Financial assets:
Equity securities	$ 28.3
Financial liabilities:
Interest rate	5.625%
Senior notes | 5.625% Notes
Financial liabilities:
Interest rate	5.625%		5.625%
Carrying Amount | Recurring
Financial assets:
Cash and cash equivalents	$ 406.9	$ 479.6
Equity securities	28.3
Held-to-maturity securities	7.5	7.5
Promissory notes	16.9	16.9
Financial liabilities:
Other liabilities	20.3	21.9
Carrying Amount | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	1,966.3	1,907.9
Carrying Amount | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	399.4	399.3
Carrying Amount | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	89.2	104.6
Fair Value | Recurring
Financial assets:
Cash and cash equivalents	406.9	479.6
Equity securities	28.3
Held-to-maturity securities	7.8	7.9
Promissory notes	17.3	17.4
Financial liabilities:
Other liabilities	20.3	21.8
Fair Value | Recurring | Secured credit facility
Financial liabilities:
Long-term debt	2,000.5	1,886.3
Fair Value | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	411.0	360.0
Fair Value | Recurring | Other long-term obligations
Financial liabilities:
Long-term debt	82.5	96.3
Level 1 | Recurring
Financial assets:
Cash and cash equivalents	406.9	479.6
Equity securities	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	2,000.5	1,886.3
Level 1 | Recurring | Senior notes | 5.625% Notes
Financial liabilities:
Long-term debt	411.0	360.0
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	28.3
Held-to-maturity securities	7.8	7.9
Promissory notes	17.3	17.4
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	82.5	96.3
Level 3 | Recurring
Financial assets:
Cash and cash equivalents	0.0	0.0
Equity securities	0.0
Held-to-maturity securities	0.0	0.0
Promissory notes	0.0	0.0
Financial liabilities:
Other liabilities	17.5	19.0
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