Unit Based Awards - Summary of restricted unit activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Restricted Units
Number of Units
Non-vested, beginning of period, numbers of units (in shares) | shares	624,125
Vested, number of units (in shares) | shares	(107,762)
Forfeited, number of units (in shares) | shares	(154,288)
Non-vested, end of period, number of units (in shares) | shares	379,019
Weighted Average Grant-Date Fair Value Per Unit
Non-vested, beginning of period, weighted average grant-date fair value per unit (in dollars per share) | $ / shares	$ 13.78
Vested, weighted average grant-date fair value per unit (in dollars per share) | $ / shares	13.82
Forfeited, weighted average grant-date fair value per unit (in dollars per share) | $ / shares	13.90
Non-vested, end of period, weighted average grant-date fair value per unit (in dollars per share) | $ / shares	$ 13.91
Aggregate intrinsic value, end of period | $	$ 1,527
Time Based Restricted Units
Number of Units
Issuance of performance-based restricted units (in shares) | shares	16,944
Weighted Average Grant-Date Fair Value Per Unit
Granted, weighted average grant-date fair value per unit (in dollars per share) | $ / shares	$ 12.45