Guarantees (Details 3)	Mar. 31, 2018 USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 134,800,000
Fixed maximum amounts guaranteed by year 2018	2,700,000
Fixed maximum amounts guaranteed by year 2019	63,000,000.0
Fixed maximum amounts guaranteed by year 2020	62,100,000
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	34,000,000.0
Letters of credit set to expire - 2018	33,300,000
Letters of credit set to expire - 2019	700,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	738,700,000
Financial guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 55,100,000