Commitments and Contingencies Available Lines of Credit, Outstanding Standby Letter of Credits, and Bonds (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Jun. 23, 2015
Line of Credit Facility [Line Items]
Multicurrency revolving line of credit			$ 500,000
Line of Credit Facility, Capacity remaining to support letters of credit	$ 220,905	$ 203,897
Credit Facility [Member]
Line of Credit Facility [Line Items]
Multicurrency revolving line of credit	500,000	500,000
Long-term Line of Credit	124,523	97,167
Letters of Credit Outstanding, Amount	(29,095)	(46,103)
Unsecured Multicurrency Revolving Lines of Credit [Member]
Line of Credit Facility [Line Items]
Multicurrency revolving line of credit	110,055	91,809
Letters of Credit Outstanding, Amount	(20,859)	(21,734)
Short-term borrowings	(2,423)	(69)
Line of Credit Facility, Remaining Borrowing Capacity	86,773	70,006
Surety Bond [Member]
Line of Credit Facility [Line Items]
Unsecured surety bonds in force	52,278	48,221
Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	124,523	97,167
Line of Credit Facility, Remaining Borrowing Capacity	$ 346,382	$ 356,730