Guarantees (Details 5)	Dec. 31, 2018 USD ($)
Guarantor Obligations [Line Items]
Fixed maximum amounts guaranteed by year 2019	$ 85,300,000
Fixed maximum amounts guaranteed by year 2020	104,000,000.0
Fixed maximum amounts guaranteed by year 2021	500,000
Fixed maximum amounts guaranteed by year 2022	500,000
Fixed maximum amounts guaranteed by year 2023	500,000
Fixed maximum amounts guaranteed, thereafter	1,500,000
Fixed maximum amounts guaranteed by year no maturity date	4,000,000.0
Amount outstanding under guarantees	0
Letters of credit	30,000,000.0
Letters of credit set to expire by year 2019	6,700,000
Letters of Credit Set to Expire by Year 2020	23,300,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	697,900,000
Financial guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 196,300,000