Fair Value of Financial Instruments (The Waha JVs) (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) pipeline	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) pipeline	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, equity in earnings (losses)	$ 6,966,000	$ 7,671,000	$ 19,778,000	$ 19,080,000
Unrealized gains (losses) on equity investee activity, net of tax	(7,108,000)	3,137,000	(21,302,000)	13,790,000
Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, net investment	$ 184,000,000		$ 184,000,000		$ 197,000,000
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	$ 0	0	$ 1,300,000	24,500,000
Equity method investments, equity in earnings (losses)	6,900,000	7,700,000	19,800,000	19,100,000
Equity method investments, cumulative undistributed earnings	42,200,000		42,200,000
Equity method investments, distributions of earnings received, operating cash flows	1,500,000	3,200,000	7,500,000	10,900,000
Unrealized gains (losses) on equity investee activity, before tax	(9,400,000)	4,100,000	(28,200,000)	18,100,000
Unrealized gains (losses) on equity investee activity, net of tax	(7,100,000)	$ 3,100,000	(21,300,000)	$ 13,800,000
Waha JVs [Member] | Equity Investee [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, net investment	$ 162,000,000		$ 162,000,000		$ 168,000,000