Guarantees (Details 3)	Sep. 30, 2018 USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 197,200,000
Fixed maximum amounts guaranteed by year 2018	1,100,000
Fixed maximum amounts guaranteed by year 2019	114,900,000
Fixed maximum amounts guaranteed by year 2020	74,200,000
Fixed maximum amounts guaranteed by year 2021	500,000
Fixed maximum amounts guaranteed by year 2022	500,000
Fixed maximum amounts guaranteed, thereafter	2,000,000.0
No scheduled maturity date	4,000,000.0
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	29,500,000
Letters of credit set to expire - 2018	28,000,000.0
Letters of credit set to expire - 2019	1,500,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	619,600,000
Financial guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 49,900,000