Commitments and Contingent Liabilities (Schedule of Commitment Expiration) (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Guarantor Obligations [Line Items]
Total Amounts Committed	$ 705,478
Less Than 1 Year	614,605
1-3 Years	88,738
3-5 Years	1,554
Beyond 5 Years	581
Letters of Credit
Guarantor Obligations [Line Items]
Total Amounts Committed	106,601
Less Than 1 Year	66,861
1-3 Years	39,740
3-5 Years	0
Beyond 5 Years	0
Letters of Credit | Employee-Related
Guarantor Obligations [Line Items]
Total Amounts Committed	73,383
Less Than 1 Year	59,241
1-3 Years	14,142
3-5 Years	0
Beyond 5 Years	0
Letters of Credit | Environmental
Guarantor Obligations [Line Items]
Total Amounts Committed	398
Less Than 1 Year	0
1-3 Years	398
3-5 Years	0
Beyond 5 Years	0
Letters of Credit | Other
Guarantor Obligations [Line Items]
Total Amounts Committed	32,820
Less Than 1 Year	7,620
1-3 Years	25,200
3-5 Years	0
Beyond 5 Years	0
Surety Bonds
Guarantor Obligations [Line Items]
Total Amounts Committed	574,791
Less Than 1 Year	539,194
1-3 Years	35,597
3-5 Years	0
Beyond 5 Years	0
Surety Bonds | Employee-Related
Guarantor Obligations [Line Items]
Total Amounts Committed	104,033
Less Than 1 Year	102,733
1-3 Years	1,300
3-5 Years	0
Beyond 5 Years	0
Surety Bonds | Environmental
Guarantor Obligations [Line Items]
Total Amounts Committed	465,837
Less Than 1 Year	431,695
1-3 Years	34,142
3-5 Years	0
Beyond 5 Years	0
Surety Bonds | Other
Guarantor Obligations [Line Items]
Total Amounts Committed	4,921
Less Than 1 Year	4,766
1-3 Years	155
3-5 Years	0
Beyond 5 Years	0
Guarantees
Guarantor Obligations [Line Items]
Total Amounts Committed	24,086
Less Than 1 Year	8,550
1-3 Years	13,401
3-5 Years	1,554
Beyond 5 Years	581
Guarantees | Other
Guarantor Obligations [Line Items]
Total Amounts Committed	24,086
Less Than 1 Year	8,550
1-3 Years	13,401
3-5 Years	1,554
Beyond 5 Years	$ 581