Fair Value of Financial Instruments (The Waha JVs) (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	$ 21,328,000	$ 3,528,000	$ (7,978,000)
Unrealized gains (losses) on equity investee activity, net of tax	475,000	3,952,000	0
Credit Facility [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Letters of credit issued	$ 157,100,000	314,300,000
Waha JVs [Member] | Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Number of pipelines in operation	2
Equity investments, equity and other contributions	$ 73,000,000	27,000,000
Equity investments, net contributions			0
Net investment, equity investments	121,000,000	6,000,000
Revenue, related parties	256,100,000	245,000,000
Receivables, including retainage, net of BIEC, related parties	2,800,000	71,200,000
Waha JVs [Member] | Equity Investee [Member] | Interest Rate Swap [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity in earnings (losses) of unconsolidated affiliates			(4,400,000)
Unrealized gains (losses) on equity investee activity	800,000	6,400,000
Unrealized gains (losses) on equity investee activity, net of tax	500,000	4,000,000
Waha JVs [Member] | Equity Investee [Member] | Other [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity in earnings (losses) of unconsolidated affiliates	21,300,000		$ (4,400,000)
Waha JVs [Member] | Equity Investee [Member] | Credit Facility [Member] | Commercial and/or Financial Standby [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Letters of credit issued	$ 19,000,000	$ 91,000,000