Debt and Interest Expense (Tables)

12 Months Ended

Dec. 31, 2018

Debt Instruments [Abstract]

Debt Outstanding and Debt Activity Tables

The following table presents WES and WGP’s outstanding debt:

	December 31, 2018						December 31, 2017
thousands	Principal		Carrying Value		Fair Value(1)		Principal		Carrying Value		Fair Value (1)
Short-term debt
WGP RCF	$	28,000	$	28,000	$	28,000	$	—	$	—	$	—
WGP long-term debt
WGP RCF	$	—	$	—	$	—	$	28,000	$	28,000	$	28,000
WES long-term debt
2.600% Senior Notes due 2018	—		—		—		350,000		349,684		350,631
5.375% Senior Notes due 2021	500,000		496,959		515,990		500,000		495,815		530,647
4.000% Senior Notes due 2022	670,000		669,078		662,109		670,000		668,849		684,043
3.950% Senior Notes due 2025	500,000		492,837		466,135		500,000		491,885		500,885
4.650% Senior Notes due 2026	500,000		495,710		483,994		500,000		495,245		520,144
4.500% Senior Notes due 2028	400,000		394,631		377,475		—		—		—
4.750% Senior Notes due 2028	400,000		395,841		384,370		—		—		—
5.450% Senior Notes due 2044	600,000		593,349		522,386		600,000		593,234		637,827
5.300% Senior Notes due 2048	700,000		686,648		605,327		—		—		—
5.500% Senior Notes due 2048	350,000		342,328		311,536		—		—		—
WES RCF	220,000		220,000		220,000		370,000		370,000		370,000
Total long-term debt	$	4,840,000	$	4,787,381	$	4,549,322	$	3,518,000	$	3,492,712	$	3,622,177

⁽¹⁾  Fair value is measured using the market approach and Level 2 inputs.

Debt activity. The following table presents WES and WGP’s debt activity for the years ended December 31, 2018 and 2017:

thousands	Carrying Value
Balance at December 31, 2016	$	3,119,461
WES RCF borrowings	370,000
Other	3,251
Balance at December 31, 2017	$	3,492,712
WES RCF borrowings	540,000
Issuance of 4.500% Senior Notes due 2028	400,000
Issuance of 5.300% Senior Notes due 2048	700,000
Issuance of 4.750% Senior Notes due 2028	400,000
Issuance of 5.500% Senior Notes due 2048	350,000
Repayment of 2.600% Senior Notes due 2018	(350,000		)
Repayments of WES RCF borrowings	(690,000		)
Other	(27,331		)
Balance at December 31, 2018	$	4,815,381

Interest-Rate Swap Table

The following interest-rate swaps were outstanding as of December 31, 2018:

Notional Principal Amount	Reference Period	Mandatory Termination Date	Fixed Interest Rate
$250.0 million	December 2019 - 2024	December 2019	2.730%
$250.0 million	December 2019 - 2029	December 2019	2.856%
$250.0 million	December 2019 - 2049	December 2019	2.905%

Interest Expense Table

The following table summarizes the amounts included in interest expense:

	Year Ended December 31,
thousands	2018			2017			2016
Third parties
Long-term and short-term debt	$	(200,454	)	$	(143,400	)	$	(122,428	)
Amortization of debt issuance costs and commitment fees	(9,110		)	(7,970		)	(7,509		)
Capitalized interest	23,521			6,826			5,562
Total interest expense – third parties	(186,043		)	(144,544		)	(124,375		)
Affiliates
Deferred purchase price obligation – Anadarko (1)	—			(71		)	7,747
Total interest expense – affiliates	—			(71		)	7,747
Interest expense	$	(186,043	)	$	(144,615	)	$	(116,628	)

⁽¹⁾  See Note 3 for a discussion of the Deferred purchase price obligation - Anadarko.