CONDENSED CONSOLIDATED STATEMENTS OF PREFERRED UNITS AND PARTNERS EARNINGS (DEFICIT) (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Beginning Balance	$ (28,835)	$ (6,578)	$ 45,834	$ 91,696	$ (6,578)	$ 91,696
Cumulative effect of accounting change				(28,097)
Beginning Balance, Adjusted				63,599		63,599
Common unit awards under incentive plans	2,289	277	1,755	158
Issuance of Series A convertible preferred units, net of issuance	57,500
Net loss	(34,398)	(22,534)	(17,017)	(17,923)	(56,932)	(34,940)
Ending Balance	(3,444)	$ (28,835)	$ 30,572	$ 45,834	(3,444)	$ 30,572
Outstanding Preferred Units | Redeemable Convertible Preferred Unit
Issuance of Series A convertible preferred units, net of issuance	$ 57,500
Issuance of Series A convertible preferred units, net of issuance (in units)	52,083,333
Ending Balance	$ 57,500				$ 57,500
Ending Balance (in units)	52,083,333				52,083,333
Outstanding Common Units
Beginning Balance (in units)	38,260,471	37,958,645	37,958,645	37,957,936	37,958,645	37,957,936
Common unit awards under incentive plans (in units)	1,273,376	301,826		709
Ending Balance (in units)	39,533,847	38,260,471	37,958,645	37,958,645	39,533,847	37,958,645
Common Limited Partners
Beginning Balance	$ (24,593)	$ (2,570)	$ 49,272	$ 94,655	$ (2,570)	$ 94,655
Cumulative effect of accounting change				(27,805)
Beginning Balance, Adjusted				66,850		66,850
Common unit awards under incentive plans	2,287	277	1,755	158
Net loss	(34,041)	(22,300)	(16,840)	(17,736)
Ending Balance	(56,347)	(24,593)	34,187	49,272	(56,347)	34,187
General Partner
Beginning Balance	(4,242)	(4,008)	(3,438)	(2,959)	(4,008)	(2,959)
Cumulative effect of accounting change				(292)
Beginning Balance, Adjusted				(3,251)		(3,251)
Common unit awards under incentive plans	2
Net loss	(357)	(234)	(177)	(187)
Ending Balance	$ (4,597)	$ (4,242)	$ (3,615)	$ (3,438)	$ (4,597)	$ (3,615)