Investments in unconsolidated entities - Other long-term investments (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Investments in unconsolidated entities
Other long-term investments	$ 388,000,000.0	$ 346,800,000
Equity method investments	0	0
Investments in unconsolidated entities
Investments in unconsolidated entities
Other long-term investments	388,000,000.0	346,800,000
Investments in unconsolidated entities | Equity method eligible investments
Investments in unconsolidated entities
Other long-term investments	166,800,000	151,900,000
Investments in unconsolidated entities | Equity method ineligible investments
Investments in unconsolidated entities
Other long-term investments	$ 221,200,000	$ 194,900,000