Commitments and Contingent Liabilities - Amount of Commitment Expiration Per Period (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	$ 310,911
Less Than 1  Year
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	306,871
1-3 Years
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	4,040
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	197,889
Standby Letters of Credit | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	6,950
Standby Letters of Credit | Loss Contingencies by Secondary Nature of Contingency
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	204,839
Standby Letters of Credit | Less Than 1  Year | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	196,917
Standby Letters of Credit | Less Than 1  Year | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	6,950
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	203,867
Standby Letters of Credit | 1-3 Years | Firm Transportation
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	972
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	972
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	9,322
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	12,480
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	106,072
Surety Bond | Less Than 1  Year | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	8,129
Surety Bond | Less Than 1  Year | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	2,600
Surety Bond | Less Than 1  Year | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	10,605
Surety Bond | Less Than 1  Year | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	81,670
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	103,004
Surety Bond | 1-3 Years | Other
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,193
Surety Bond | 1-3 Years | Employee-Related
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
Surety Bond | 1-3 Years | Environmental
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	1,875
Surety Bond | 1-3 Years | Financial Guarantees
Schedule of Costs Related to Purchase Obligations [Line Items]
Guarantor obligations, maximum exposure	0
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	3,068
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