Commitments and Contingent Liabilities - Amount of Commitment Expiration Per Period (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	$ 303,175
Less Than 1 Year
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	126,900
1-3 Years
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	176,275
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
Standby Letters of Credit | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	198,316
Standby Letters of Credit | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	750
Standby Letters of Credit | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	199,066
Standby Letters of Credit | Less Than 1 Year | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	80,244
Standby Letters of Credit | Less Than 1 Year | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	750
Standby 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	80,994
Standby Letters of Credit | 1-3 Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	118,072
Standby Letters of Credit | 1-3 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Standby 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	118,072
Standby Letters of Credit | 3-5 Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Standby Letters of Credit | 3-5 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Standby 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
Standby Letters of Credit | Beyond 5 Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Standby Letters of Credit | Beyond 5 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Standby 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	9,306
Surety Bond | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,850
Surety Bond | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	11,283
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	104,109
Surety Bond | Less Than 1 Year | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	8,433
Surety Bond | Less Than 1 Year | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | Less Than 1 Year | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	11,073
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	45,906
Surety Bond | 1-3 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	873
Surety Bond | 1-3 Years | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,850
Surety Bond | 1-3 Years | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	210
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	58,203
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