Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Cash flows from operating activities:
Net income		$ 58,867	$ 56,805		$ 16,108	[1],[2]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		5,111	5,647		5,828	[1],[2]
Accretion		238	236		201	[1]
Amortization of debt issuance costs		492	299		134	[1]
Increase in deferred lease liability		58	390		20	[1]
Deferred income taxes		20	(2)		(4,076)	[1]
Unit-based compensation		219	143		67	[1]
Undistributed equity loss		11
Changes in operating assets and liabilities:
Accounts receivable		(1,127)	(947)		(82)	[1]
Accounts receivable from affiliates		1,443	(4,430)		(13,283)	[1]
Prepaid expenses and other assets		58	(44)		(404)	[1]
Accounts payable and accrued liabilities		(1,494)	3,703		10,352	[1]
Accounts payable to affiliates		185	383		960	[1]
Other		(27)	12		(92)	[1]
Net cash provided by operating activities		64,054	62,195		15,733	[1]
Cash flows from investing activities
Purchases of property and equipment, net		(1,914)	(537)		(1,497)	[1]
Equity method investment		(2,248)
Acquisition of assets from sponsor			(62,312)
Acquisition of assets			(90,000)
Proceeds on disposal of assets, net	[1]				19
Net cash used by investing activities		(4,162)	(152,849)		(1,478)	[1]
Cash flows from financing activities
Proceeds from initial public offering, net	[1]				157,452
Payments of distributions		(57,771)	(53,125)		(168,275)	[1]
Proceeds from revolving credit facility		70,100	218,000
Payments on revolving credit facility		(72,200)	(89,000)
Payments of loan fees		(146)	(987)		(875)	[1]
Member contributions, net	[1]				8,123
Other		5	3
Net cash provided (used) by financing activities		(60,012)	74,891		(3,575)	[1]
Net change in cash and cash equivalents		(120)	(15,763)		10,680	[1]
Cash and cash equivalents, beginning of period		622	16,385	[1]	5,705	[1]
Cash and cash equivalents, end of period		502	622		16,385	[1]
Supplemental disclosures of cash flow:
Cash paid for income taxes		143	248		1,006	[1]
Cash paid for interest		$ 4,973	$ 2,189		$ 173	[1]

[1] Recast to include historical cash flow activity related to net assets acquired in a transfer between entities under common control. See Notes 1 and 4 in the accompanying notes to consolidated financial statements for further discussion.

[2] Recast to include historical results of operations related to net assets acquired in a transfer between entities under common control. See Notes 1 and 4 in the accompanying notes to consolidated financial statements for further discussion.