Investments in unconsolidated entities - Other long-term investments (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Investments in unconsolidated entities
Other long-term investments	$ 355,500,000	$ 346,800,000
Equity method investments	0	0
Investments in unconsolidated entities
Investments in unconsolidated entities
Other long-term investments	355,500,000	346,800,000
Investments in unconsolidated entities | Equity method eligible investments
Investments in unconsolidated entities
Other long-term investments	151,800,000	151,900,000
Investments in unconsolidated entities | Equity method ineligible investments
Investments in unconsolidated entities
Other long-term investments	$ 203,700,000	$ 194,900,000