CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 265.4	$ 272.9	$ 148.9
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation, amortization and accretion	23.7	21.6	18.4
Loss from disposition of fixed assets	0.1	0.0	0.2
Non-cash interest expense	2.7	0.0	0.0
Allowance oil reduction to net realizable value	0.0	1.6	4.4
Undistributed equity earnings	1.8	(0.6)	(0.5)
Changes in operating assets and liabilities
Accounts receivable	0.1	0.0	(14.4)
Allowance oil	(4.8)	(2.8)	2.4
Prepaid expenses	(1.0)	(1.2)	(1.5)
Accounts payable	(1.5)	(4.5)	7.6
Deferred revenue and other unearned income	8.2	(13.8)	20.0
Accrued liabilities	(1.7)	9.5	(18.5)
Net cash provided by operating activities	293.0	282.7	167.0
Cash flows from investing activities
Capital expenditures	(28.3)	(16.2)	(68.7)
Acquisitions	(214.8)	(179.8)	0.0
Payment of pre-IPO distributions from investments to SPLC	15.0	6.8	2.1
Payment of pre-IPO distributions from investments to SPLC	0.0	(11.9)	5.1
Net cash used in investing activities	(228.1)	(201.1)	(61.5)
Cash flows from financing activities
Net proceeds from IPO, net of offering costs of $46.3 million	0.0	0.0	1,011.7
Net proceeds from private equity placement	0.0	297.4	0.0
Net proceeds from public equity offerings	818.1	296.8	0.0
Borrowings under credit facilities	638.7	458.2	0.0
Contributions from general partner	9.8	6.1	0.0
Repayment of credit facilities	(410.0)	0.0	0.0
Proceeds from IPO distributed to Parent	0.0	0.0	(911.7)
Capital distributions to general partner	(896.3)	(1,002.1)	0.0
Distributions to noncontrolling interest	(20.3)	(67.1)	(25.2)
Distributions to unitholders and general partner	(179.9)	(96.5)	0.0
Other contributions from Parent	4.6	11.1	0.0
Credit facilities issuance costs	(0.6)	(0.3)	(0.5)
Capital lease payments	(0.1)	0.0	0.0
Net distributions to Parent	0.0	(42.4)	(27.8)
Distribution of working capital to Parent	0.0	0.0	(1.8)
Net cash (used in) provided by financing activities	(36.0)	(138.8)	44.7
Net increase (decrease) in cash and cash equivalents	28.9	(57.2)	150.2
Cash at beginning of the year	93.0	150.2	0.0
Cash at end of the year	121.9	93.0	150.2
Non-cash investing and financing transactions:
Change in accrued capital expenditures	0.5	2.9	(13.1)
Contribution of fixed assets from Parent	0.0	0.4	11.4
Amount payable to SPLC for pre-IPO distribution	0.0	0.0	(6.8)
Contribution of investments upon IPO	0.0	0.0	166.0
Commencement of capital lease	0.0	22.8	0.0
Other non-cash contributions from Parent	0.2	1.8	0.0
Other non-cash capital distributions to general partner	(7.1)	0.0	0.0
Other non-cash contribution from general partner	7.1	0.0	0.0
Distribution of working capital to Parent	$ 0.0	$ (6.4)	$ 0.0