Fair Value of Financial Instruments (The Waha JVs) (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) pipeline	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) pipeline	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, equity in earnings (losses)	$ 5,824,000	$ 6,060,000	$ 11,409,000	$ 7,706,000
Unrealized gains (losses) on equity method investee activity, net of tax	2,937,000	(2,730,000)	10,653,000	(2,095,000)
Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, net investment	190,000,000		190,000,000		$ 141,000,000
Credit Facility [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Letters of credit issued	$ 124,700,000		$ 124,700,000		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		2
Equity method investments, equity contributions	$ 9,700,000	19,900,000	$ 24,500,000	73,300,000
Equity method investments, equity in earnings (losses)	5,800,000	6,100,000	11,400,000	7,700,000
Equity method investments, cumulative undistributed earnings	20,600,000		20,600,000
Equity method investments, distributions of earnings received	2,000,000		7,700,000
Revenue, related parties		100,200,000		251,600,000
Receivables, net of BIEC, related parties	200,000		200,000		2,800,000
Unrealized gains (losses) on equity method investee activity	3,900,000	(4,400,000)	14,000,000	(3,400,000)
Unrealized gains (losses) on equity method investee activity, net of tax	2,900,000	$ (2,700,000)	10,700,000	$ (2,100,000)
Waha JVs [Member] | Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, net investment	160,000,000		160,000,000		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		$ 0		$ 19,000,000