Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 43,347	$ 32,706	$ 32,908
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	39,242	35,384	28,934
Reserve for doubtful accounts	26	(1)	88
Amortization of loan fees	1,556	1,271	523
Unit-based compensation expense	2,659	2,000	1,564
Deferred income taxes	641	0	0
Loss (gain) and impairments on disposal of assets, net	(1,054)	(278)	157
Accounts receivable - Third-party	(10,213)	(267)	(54,377)
Accounts receivable - Affiliate	(4,615)	8,042	(40,625)
Inventories	5,056	(717)	1,799
Prepaid expenses	(2,288)	4,143	(1,466)
Other assets	(660)	(2,770)	(3,507)
Accounts payable and accrued liabilities	34,483	(6,976)	123,372
Other long-term liabilities	0	9	(5)
Net cash provided by operating activities	108,180	72,546	89,365
Cash flows from investing activities:
Capital expenditures	(30,308)	(67,625)	(79,338)
Proceeds from sale of assets	5,303	506	106
Net cash used in investing activities	(25,005)	(67,119)	(79,232)
Cash flows from financing activities:
Additions to long-term debt	0	300,000	0
Borrowings on revolving credit facility	54,400	145,000	269,000
Payments on revolving credit facility	(179,100)	(269,000)	0
Proceeds from issuance of common units	277,751	0	0
Offering costs for issuance of common units	(655)	0	0
Quarterly distribution to Western	(56,189)	(45,455)	(35,042)
Quarterly distribution to common unitholders - public	33,203	22,629	18,394
Deferred financing costs	(1,224)	(6,820)	0
Contributions from affiliate	20,092	53,784	64,597
Distribution to Western due to acquisitions	195,000	170,000	320,000
Net cash used in financing activities	(113,128)	(15,120)	(39,839)
Net change in cash and cash equivalents	(29,953)	(9,693)	(29,706)
Cash and cash equivalents at beginning of year	44,605	54,298	84,004
Cash and cash equivalents at end of year	$ 14,652	$ 44,605	$ 54,298