Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 130,098	$ 116,580
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation expense	37,405	24,280
Changes in current assets and current liabilities	6,101	(734)
Changes in deferred charges and credits and other operating activities, net	1,553	856
Net cash provided by operating activities	175,157	140,982
Cash flows from investing activities:
Capital expenditures	(13,083)	(15,240)
Other investing activities, net	8	8
Net cash used in investing activities	(13,075)	(87,025)
Cash flows from financing activities:
Proceeds from issuance of senior notes	498,300	0
Repayment of debt and note payable – related party	(495,000)	0
Payment of debt issuance costs	(4,464)	(492)
Proceeds from issuance of common units	0	35,728
Proceeds from issuance of general partner units	5	748
Payment of offering costs	0	(517)
Cash distributions to unitholders and distribution equivalent right payments	(102,881)	(72,938)
Net cash used in financing activities	(104,040)	(37,471)
Net increase in cash and cash equivalents	58,042	16,486
Cash and cash equivalents at beginning of period	42,052	71,491
Cash and cash equivalents at end of period	100,094	87,977
Red River Crude System [Member]
Cash flows from investing activities:
Acquisition of undivided interest in Red River crude system	$ 0	$ (71,793)