Consolidated Statements of Cash Flows - WES Operating - USD ($) $ in Thousands		3 Months Ended						9 Months Ended				12 Months Ended
		Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018		Mar. 31, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2018
Cash flows from operating activities
Net income (loss)		$ 125,223	$ 211,979	$ 198,560	[1]	$ 181,010	[1]	$ 512,260		$ 446,737	[1]
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization		127,914		97,479	[1]			362,977		270,757	[1]
Impairments		3,107		27,902	[1]			4,294		155,286	[1]	$ 230,600
Non-cash equity-based compensation expense								9,489		4,834	[1]
Deferred income taxes								6,601		83,295	[1]
Accretion and amortization of long-term obligations, net								6,499		4,659	[1]
Equity income, net – affiliates		(53,893)		(54,215)	[1]			(175,483)		(133,874)	[1]
Distributions from equity investment earnings – affiliates								182,337		125,834	[1]
(Gain) loss on divestiture and other, net		(248)		(65)	[1]			1,403		(351)	[1]
(Gain) loss on interest-rate swaps								162,974		0	[1]
Lower of cost or market inventory adjustments								236		184	[1]
Changes in assets and liabilities:
(Increase) decrease in accounts receivable, net								(9,750)		(64,853)	[1]
Increase (decrease) in accounts and imbalance payables and accrued liabilities, net								(69,390)		61,081	[1]
Change in other items, net								32,238		11,606	[1]
Net cash provided by operating activities								1,026,685		965,195	[1]
Cash flows from investing activities
Capital expenditures								(947,266)		(1,589,653)	[1]
Investments in equity affiliates								(108,118)		(67,085)	[1]
Distributions from equity investments in excess of cumulative earnings – affiliates								21,203		19,816	[1]
Net cash used in investing activities								(3,134,643)		(1,798,702)	[1]
Cash flows from financing activities
Borrowings, net of debt issuance costs	[2]							3,950,750		2,401,097	[1]
Repayments of debt	[3]							(1,467,595)		(1,040,000)	[1]
Increase (decrease) in outstanding checks								(9,204)		(2,687)	[1]
Distributions to WES Operating unitholders	[4]							(688,193)		(372,189)	[1]
Net contributions from (distributions to) Anadarko								458,819		156,734	[1]
Above-market component of swap agreements with Anadarko		0		12,601				7,407	[4]	40,722	[1],[4]
Finance lease payments – affiliates								(253)
Net cash provided by (used in) financing activities								2,133,246		886,796	[1]
Net increase (decrease) in cash and cash equivalents								25,288		53,289	[1]
Cash and cash equivalents at beginning of period	[1]		92,142			79,588		92,142		79,588		79,588
Cash and cash equivalents at end of period		117,430		132,877	[1]			117,430		132,877	[1]	92,142	[1]
Supplemental disclosures
Net distributions to (contributions from) Anadarko of other assets				(58,835)	[1]			0		(58,835)	[1]
Interest paid, net of capitalized interest								232,147		106,538	[1]
Taxes paid (reimbursements received)								96		(87)	[1]
Accrued capital expenditures								154,080		296,805	[1]
Chipeta [Member]
Cash flows from financing activities
Distributions to Chipeta noncontrolling interest owner								(5,200)		(9,446)	[1]
Affiliates [Member]
Cash flows from investing activities
Acquisitions								(2,007,501)		(254)	[1]
Cash flows from financing activities
Borrowings, net of debt issuance costs								11,000		265,500
Repayments of debt								(439,600)
Distributions to WES Operating unitholders		(155,240)		(99,247)				(411,125)		(298,818)
Finance lease payments – affiliates								(253)		0	[1]
Third Parties [Member]
Cash flows from investing activities
Acquisitions								(93,303)		(161,858)	[1]
Proceeds from the sale of assets								342		332	[1]
WES Operating [Member]
Cash flows from operating activities
Net income (loss)		126,912	214,450	199,519	[1]	182,870	[1]	518,341		450,512	[1]
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization		127,914		97,479	[1]			362,977		270,757	[1]
Impairments		3,107		27,902	[1]			4,294		155,286	[1]
Non-cash equity-based compensation expense								8,234		4,620	[1]
Deferred income taxes								6,601		83,295	[1]
Accretion and amortization of long-term obligations, net								6,479		3,883	[1]
Equity income, net – affiliates		(53,893)		(54,215)	[1]			(175,483)		(133,874)	[1]
Distributions from equity investment earnings – affiliates								182,337		125,834	[1]
(Gain) loss on divestiture and other, net		(248)		(65)	[1]			1,403		(351)	[1]
(Gain) loss on interest-rate swaps								162,974		0	[1]
Lower of cost or market inventory adjustments								236		184	[1]
Changes in assets and liabilities:
(Increase) decrease in accounts receivable, net								(12,219)		(64,707)	[1]
Increase (decrease) in accounts and imbalance payables and accrued liabilities, net								(68,277)		60,956	[1]
Change in other items, net								34,232		11,143	[1]
Net cash provided by operating activities								1,032,129		967,538	[1]
Cash flows from investing activities
Capital expenditures								(947,266)		(1,589,653)	[1]
Investments in equity affiliates								(108,118)		(67,085)	[1]
Distributions from equity investments in excess of cumulative earnings – affiliates								21,203		19,816	[1]
Net cash used in investing activities								(3,134,643)		(1,798,702)	[1]
Cash flows from financing activities
Borrowings, net of debt issuance costs	[5]							3,950,750		2,401,105	[1]
Repayments of debt	[6]							(1,439,595)		(1,040,000)	[1]
Increase (decrease) in outstanding checks								(9,204)		(2,687)	[1]
Distributions to WES Operating unitholders	[7]							(834,712)		(663,410)	[1]
Net contributions from (distributions to) Anadarko								458,819		156,734	[1]
Above-market component of swap agreements with Anadarko	[7]							7,407		40,722	[1]
Net cash provided by (used in) financing activities								2,128,012		883,018	[1]
Net increase (decrease) in cash and cash equivalents								25,498		51,854	[1]
Cash and cash equivalents at beginning of period	[1]		$ 90,448			$ 78,814		90,448		78,814		78,814
Cash and cash equivalents at end of period		115,946		130,668	[1]			115,946		130,668	[1]	$ 90,448	[1]
Supplemental disclosures
Net distributions to (contributions from) Anadarko of other assets				(58,835)	[1]			0		(58,835)	[1]
Interest paid, net of capitalized interest								231,913		105,615	[1]
Taxes paid (reimbursements received)								96		(87)	[1]
Accrued capital expenditures								154,080		296,805	[1]
WES Operating [Member] | Chipeta [Member]
Cash flows from financing activities
Distributions to Chipeta noncontrolling interest owner								(5,200)		(9,446)	[1]
WES Operating [Member] | Affiliates [Member]
Cash flows from investing activities
Acquisitions								(2,007,501)		(254)	[1]
Cash flows from financing activities
Borrowings, net of debt issuance costs								11,000		265,500
Repayments of debt								(439,600)
Distributions to WES Operating unitholders		$ (288,083)		$ (130,249)				(736,256)		(381,617)
Finance lease payments – affiliates								(253)		0	[1]
WES Operating [Member] | Third Parties [Member]
Cash flows from investing activities
Acquisitions								(93,303)		(161,858)	[1]
Proceeds from the sale of assets								$ 342		$ 332	[1]

[1] Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

[2] For the nine months ended September 30, 2019 and 2018, includes $11.0 million and $265.5 million of borrowings, respectively, under the APCWH Note Payable.

[3] For the nine months ended September 30, 2019, includes a $439.6 million repayment to settle the APCWH Note Payable. See Note 6.

[4] See Note 6.

[5] For the nine months ended September 30, 2019 and 2018, includes $11.0 million and $265.5 million of borrowings, respectively, under the APCWH Note Payable.

[6] For the nine months ended September 30, 2019, includes a $439.6 million repayment to settle the APCWH Note Payable. See Note 6.

[7] See Note 6.