Guarantees (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Guarantor Obligations [Line Items]
Maximum Potential Payment	$ 13,891
Carrying Amount of Liability	43
Standy letters of credit
Guarantor Obligations [Line Items]
Maximum Potential Payment	10,353
Carrying Amount of Liability	0
Standy letters of credit | Bonds
Guarantor Obligations [Line Items]
Letter of credit for development project	9,200
Guarantees
Guarantor Obligations [Line Items]
Maximum Potential Payment	2,254
Carrying Amount of Liability	43
Surety bonds
Guarantor Obligations [Line Items]
Maximum Potential Payment	1,284
Carrying Amount of Liability	$ 0