Equity-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Nonvested unit activity (table)
Nonvested units outstanding at December 31, 2012	155,000
Nonvested units outstanding, weighted average grant date fair value per unit	$ 17.52
Units granted	208,671	97,713	94,728
Units granted, weighted average grant date fair value per unit	$ 22.89	$ 20.29	$ 13.68
Units granted, aggregate fair market value	$ 4,800,000	$ 2,000,000	$ 1,300,000
Units cancelled	(21,000)
Units cancelled, weighted average grant date fair value per unit	$ 18.97
Units vested	(74,000)
Units vested, weighted average grant date fair value per unit	$ 18.27
Units vested, aggregate fair market value	1,300,000	1,300,000	1,200,000
Adjustment for performance results achieved	(6,000)
Adjustment for performance results achieved, weighted average grant date fair value	$ 24.00
Nonvested units outstanding at December 31, 2013	263,000	155,000
Nonvested units outstanding, weighted average grant date fair value per unit	$ 21.90	$ 17.52
Maximum number of performance-based units that may be earned under awards granted	93,630
Minimum number of performance-based units that may be earned under awards granted	0
Equity compensation expense	1,544,000	1,459,000	1,905,000
Estimated unrecognized equity-based compensation expense	$ 2,900,000
Weighted average period of recognition	1 year 255 days