Fair Value of Financial Instruments (The Waha JVs) (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, equity in earnings (losses)	$ 29,738,000	$ 27,367,000	$ 23,855,000
Equity method investments, net investment	220,000,000	196,000,000
Unrealized gains (losses) on equity investee activity, net of tax	(17,151,000)	(15,023,000)	5,863,000
Waha JVs [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, equity in earnings (losses)	31,300,000	27,300,000	23,900,000
Equity method investments, distributions of earnings received, operating cash flows	12,000,000.0	9,100,000	10,900,000
Equity method investments, cumulative undistributed earnings	67,300,000
Equity method investments, equity contributions	0	1,000,000	28,000,000
Equity method investments, net investment	175,000,000	174,000,000
Unrealized gains (losses) on equity investee activity, before tax	(24,400,000)	(19,900,000)	7,700,000
Unrealized gains (losses) on equity investee activity, net of tax	$ (18,500,000)	$ (15,000,000.0)	$ 5,900,000