Long-Term Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

The amounts below do not include adjustments for above-target or below-target performance.



	Performance-Based Awards				Time-Based Awards				Total Awards
	Number of Unit Awards		Weighted-Average Fair Value		Number of Unit Awards		Weighted-Average Fair Value		Number of Unit Awards		Weighted-Average Fair Value
Non-vested units - 1/1/2017	313,696		$	78.03	82,418		$	75.36	396,114		$	77.47
Units granted during 2017	189,544		$	82.34	30,604		$	79.10	220,148		$	81.89
Units vested during 2017	(128,333	)	$	88.75	(50,099	)	$	82.46	(178,432	)	$	86.99
Units forfeited during 2017	(18,839	)	$	79.11	(1,819	)	$	77.05	(20,658	)	$	78.93
Non-vested units - 12/31/17	356,068		$	76.40	61,104		$	71.36	417,172		$	75.66

Total Non-Vested Unit Awards

The table below summarizes the total non-vested unit awards outstanding adjusted for estimated amounts of above-target financial performance to determine the total number of unit awards included in our total equity-based liability accrual.



Grant Date	Non-Vested Unit Awards	Adjustment to Unit Awards in Anticipation of Achieving Above- Target Financial Results	Total Unit Award Accrual	Vesting Date	Unrecognized Compensation Expense^(a) (in millions)
Performance-Based Awards:
2016 Awards	175,445	43,861	219,306	12/31/2018	$	5.0
2017 Awards	180,623	—	180,623	12/31/2019	9.8
Time-Based Awards:
2018 Vesting Date	31,174	—	31,174	12/31/2018	0.7
2019 Vesting Date	28,214	—	28,214	12/31/2019	1.6
2020 Vesting Date	1,716	—	1,716	12/31/2020	0.1
Total	417,172	43,861	461,033		$	17.2

(a) Unrecognized compensation expense will be recognized over the remaining vesting period of the awards.

Weighted-Average Grant Date Fair Values

The weighted-average fair value of awards granted during 2015, 2016 and 2017 was as follows:



	Performance-Based Awards			Time-Based Awards
	Number of Unit Awards	Weighted-Average Fair Value		Number of Unit Awards	Weighted-Average Fair Value
Units granted during 2015	148,028	$	88.78	26,421	$	81.51
Units granted during 2016	193,344	$	70.29	39,301	$	64.76
Units granted during 2017	189,544	$	82.34	30,604	$	79.10

Vested Unit Awards

The table below sets forth the numbers and values of units that vested in each of the three years ended December 31, 2017. The vested limited partner units include adjustments for above-target financial and market performance.



Vesting Date	Vested Limited Partner Units	Fair Value of Unit Awards on Vesting Date (in millions)	Intrinsic Value of Unit Awards on Vesting Date (in millions)
12/31/2015	506,393	$27.7	$34.4
12/31/2016	361,711	$22.6	$27.4
12/31/2017	266,028	$19.9	$18.9

Cash Flow Effects Of Long Term Incentive Plan Settlements [Table Text Block]

The difference between the limited partner units issued to the participants and the total number of unit awards vested primarily represents the tax withholdings associated with the award settlement, which we pay in cash.



Settlement Date	Number of Limited Partner Units Issued, Net of Tax Withholdings	Tax Withholdings and Other Cash Payments (in millions)	Employer Taxes (in millions)	Total Cash Taxes Paid (in millions)
January 2015	354,529	$17.8	$1.7	$19.5
February 2016	350,552	$14.4	$1.4	$15.8
January 2017	216,679	$13.9	$1.2	$15.1

Equity-Based Incentive Compensation Expense

Equity-based incentive compensation expense for 2015, 2016 and 2017 was as follows (in thousands):



	Year Ended December 31,
	2015		2016		2017
2013 awards	$	10,658	$	—	$	—
2014 awards	7,471		7,928		28
2015 awards	4,917		4,874		6,645
2016 awards	—		4,304		6,125
2017 awards	—		—		5,025
Time-based awards	1,199		2,252		2,818
Total	$	24,245	$	19,358	$	20,641

Allocation of LTIP expense on our consolidated statements of income:
G&A expense	$	23,937	$	19,204	$	20,463
Operating expense	308		154		178
Total	$	24,245	$	19,358	$	20,641