Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands | 3 Months Ended |
Dec. 31, 2018 | Dec. 31, 2017 |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | $ 499,597 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | (528) | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | (8,822) | |
Revenue | 490,247 | $ 419,655 |
Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 174,823 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | (11,947) | |
Revenue | 162,876 | |
Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 77,069 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Revenue | 77,069 | |
Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 29,690 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Revenue | 29,690 | |
Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 223,185 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | (528) | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Revenue | 222,657 | |
Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 49,287 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | 3,125 | |
Revenue | 52,412 | |
All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 1,007 | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Revenue | 1,007 | |
Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | (55,464) | |
Alternative Revenue Programs Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Derivative Financial Instruments Outside Scope of Authoritative Guidance on Revenue Recognition | 0 | |
Revenue | (55,464) | |
Production of Natural Gas [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 135,911 | |
Production of Natural Gas [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 135,911 | |
Production of Natural Gas [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Natural Gas [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Natural Gas [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Natural Gas [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Natural Gas [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Natural Gas [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Crude Oil [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 37,555 | |
Production of Crude Oil [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 37,555 | |
Production of Crude Oil [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Crude Oil [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Crude Oil [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Crude Oil [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Crude Oil [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Production of Crude Oil [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Processing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 975 | |
Natural Gas Processing [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 975 | |
Natural Gas Processing [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Processing [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Processing [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Processing [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Processing [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Processing [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 29,690 | |
Natural Gas Gathering Services [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Gathering Services [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | (29,690) | |
Natural Gas Transportation Service [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 74,701 | |
Natural Gas Transportation Service [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Transportation Service [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 56,135 | |
Natural Gas Transportation Service [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Transportation Service [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 35,631 | |
Natural Gas Transportation Service [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Transportation Service [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Transportation Service [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | (17,065) | |
Natural Gas Storage Service [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 10,956 | |
Natural Gas Storage Service [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Storage Service [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 18,929 | |
Natural Gas Storage Service [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Storage Service [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Storage Service [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Storage Service [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Storage Service [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | (7,973) | |
Natural Gas Residential Sales [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 166,867 | |
Natural Gas Residential Sales [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Residential Sales [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Residential Sales [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Residential Sales [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 166,867 | |
Natural Gas Residential Sales [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Residential Sales [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Residential Sales [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Commercial Sales [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 22,047 | |
Natural Gas Commercial Sales [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Commercial Sales [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Commercial Sales [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Commercial Sales [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 22,047 | |
Natural Gas Commercial Sales [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Commercial Sales [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Commercial Sales [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Industrial Sales [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 1,501 | |
Natural Gas Industrial Sales [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Industrial Sales [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Industrial Sales [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Industrial Sales [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 1,501 | |
Natural Gas Industrial Sales [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Industrial Sales [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Industrial Sales [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 48,955 | |
Natural Gas Marketing [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Marketing [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Marketing [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Marketing [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Marketing [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 49,287 | |
Natural Gas Marketing [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Natural Gas Marketing [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | (332) | |
Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 129 | |
Other [Member] | Exploration And Production [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 382 | |
Other [Member] | Pipeline And Storage [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 2,005 | |
Other [Member] | Gathering [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Other [Member] | Utility [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | (2,861) | |
Other [Member] | Energy Marketing [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 0 | |
Other [Member] | All Other [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | 1,007 | |
Other [Member] | Corporate And Intersegment Eliminations [Member] | | |
Disaggregation of Revenue [Line Items] | | |
Revenue from Contracts with Customers | $ (404) | |