Commitments and Contingent Liabilities - Amount of Commitment Expiration Per Period (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	$ 291,169
Less Than 1  Year
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	232,513
1-3 Years
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	58,656
3-5 Years
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Beyond 5  Years
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	178,352
Letters of Credit | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	6,950
Letters of Credit | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	185,302
Letters of Credit | Less Than 1  Year | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	178,352
Letters of Credit | Less Than 1  Year | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	6,950
Letters of Credit | Less Than 1  Year | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	185,302
Letters of Credit | 1-3 Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | 1-3 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | 1-3 Years | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | 3-5 Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | 3-5 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | 3-5 Years | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | Beyond 5  Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | Beyond 5  Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Letters of Credit | Beyond 5  Years | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	9,285
Surety Bond | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	2,600
Surety Bond | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	12,312
Surety Bond | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	81,670
Surety Bond | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	105,867
Surety Bond | Less Than 1  Year | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	8,594
Surety Bond | Less Than 1  Year | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,500
Surety Bond | Less Than 1  Year | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	10,717
Surety Bond | Less Than 1  Year | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	26,400
Surety Bond | Less Than 1  Year | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	47,211
Surety Bond | 1-3 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	691
Surety Bond | 1-3 Years | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,100
Surety Bond | 1-3 Years | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,595
Surety Bond | 1-3 Years | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	55,270
Surety Bond | 1-3 Years | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	58,656
Surety Bond | 3-5 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | 3-5 Years | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | 3-5 Years | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | 3-5 Years | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | 3-5 Years | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Beyond 5  Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Beyond 5  Years | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Beyond 5  Years | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Beyond 5  Years | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Beyond 5  Years | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	$ 0