Equity-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Nonvested unit activity (table)
Nonvested units outstanding at December 31, 2012	609,000
Nonvested units outstanding, weighted average grant date fair value per unit	$ 13.41
Units granted	290,190	396,692	180,136
Unit-based Compensation Arrangement by Unit-based Payment Award, Equity Instruments Other than Options, Grants in Period, average market value	$ 8.40
Units granted, weighted average grant date fair value per unit	$ 8.40	$ 8.38	$ 20.35
Units granted, aggregate fair market value	$ 2,400	$ 3,300	$ 3,900
Units cancelled	(173,000)
Units cancelled, weighted average grant date fair value per unit	$ 16.11
Units vested	(257,000)
Units vested, weighted average grant date fair value per unit	$ 13.17
Units vested, aggregate fair market value	$ 2,800	$ 1,500	1,100
Nonvested units outstanding at December 31, 2013	469,000	609,000
Nonvested units outstanding, weighted average grant date fair value per unit	$ 9.31	$ 13.41
Maximum number of performance-based units that may be earned under awards granted	176,159	289,830
Performance units granted		18,226
Minimum number of performance-based units that may be earned under awards granted	0
Maximum number of performance-based units actually issued under awards granted	352,318
Equity compensation expense	$ 1,219	$ 3,028	$ 2,164
Estimated unrecognized equity-based compensation expense	$ 2,200
Weighted average period of recognition	1 year 8 months 12 days