Variable Interest Entities - Financial Data of WGP (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Statement of Operations Data
Total revenues and other		$ 3,697,000	$ 2,496,000	$ 10,033,000	$ 8,979,000
Operating income (loss)		979,000	(749,000)	2,349,000	(916,000)
Net Income (Loss)		427,000	(641,000)	618,000	(1,250,000)
Statement of Cash Flow Data
Net cash provided by (used in) operating activities				4,302,000	2,619,000
Net cash provided by (used in) investing activities				(4,659,000)	(28,000)
Net cash provided by (used in) financing activities				(2,306,000)	(527,000)
Balance Sheet Data
Cash and cash equivalents		1,883,000		1,883,000		$ 4,553,000
Net properties and equipment related to VIEs		28,744,000		28,744,000		27,451,000
Total assets		41,145,000		41,145,000		42,086,000
Long-term debt		15,755,000		15,755,000		15,547,000
Total equity		11,237,000		11,237,000		13,790,000
Variable Interest Entity, Primary Beneficiary [Member]
Balance Sheet Data
Cash and cash equivalents		133,000		133,000		80,000
Net properties and equipment related to VIEs		6,419,000		6,419,000		5,731,000
WGP [Member]
Balance Sheet Data
Long-term debt	[1]	0		0		28,000
WGP [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Statement of Operations Data
Total revenues and other		508	575	1,432	1,616
Operating income (loss)		200	179	461	523
Net Income (Loss)		155	$ 147	340	424
Statement of Cash Flow Data
Net cash provided by (used in) operating activities				749	642
Net cash provided by (used in) investing activities				(1,161)	(515)
Net cash provided by (used in) financing activities				465	$ (334)
Balance Sheet Data
Cash and cash equivalents		133		133		80
Net properties and equipment related to VIEs		6,419		6,419		5,731
Total assets		9,034		9,034		8,016
Long-term debt		4,566		4,566		3,493
Total liabilities		5,417		5,417		4,071
Total equity		$ 3,617		$ 3,617		$ 3,945

[1] Excludes WES.