Fair Value of Financial Instruments (The Waha JVs) (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) pipeline	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Letters of credit issued	$ 128,400,000	$ 157,100,000
Equity method investments, equity in earnings (losses)	23,855,000	21,328,000	$ 3,528,000
Unrealized gains on equity investee activity, net of tax	5,863,000	475,000	3,952,000
Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, net investment	197,000,000	141,000,000
Credit Facility [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Letters of credit issued	$ 88,200,000	157,100,000
Waha JVs [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Number of pipelines in operation | pipeline	2
Equity method investments, equity and other contributions	$ 28,000,000	73,000,000	27,000,000
Equity method investments, equity in earnings (losses)	23,900,000	21,300,000
Equity method investments, cumulative undistributed earnings	29,900,000
Equity method investments, distributions of earnings received, operating cash flows	10,900,000
Revenue, related parties		256,100,000	245,000,000
Receivables, net of BIEC, related parties		2,800,000
Unrealized gains on equity investee activity	7,700,000	800,000	6,400,000
Unrealized gains on equity investee activity, net of tax	5,900,000	500,000	$ 4,000,000
Waha JVs [Member] | Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, net investment	168,000,000	121,000,000
Waha JVs [Member] | Credit Facility [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Letters of credit issued	$ 0	$ 19,000,000