Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Nonvested Performance-based Units Activity

Below is a summary of our long-term incentive unit activity for the year ended December 31, 2017.

Unvested Long-term Incentive Units	Units		Weighted-Average Grant Date Fair Value
Unvested, beginning of period	128,822		$	66.58
Granted	72,664		109.71
Vested	(94,801	)	71.97
Cancelled or expired	(7,390	)	98.94
Unvested, end of period	99,295		$	90.59

Schedule of Share-based Compensation, Performance Based Awards

Level	RMS Relative Market Performance	Market Performance Vesting Percentage
Below Threshold Level	< -300 basis points	0	%
Threshold Level	-300 basis points	25	%
Target Level	100 basis points	50	%
High Level	> 500 basis points	100	%

Schedule of Share-Based Payment Award Valuation Assumptions

Assumptions used in the valuations are summarized as follows:

Award Date	Expected Stock Price Volatility	Risk-Free Interest Rate
February 24, 2015	24%	1.00%
January 1, 2016	22%	1.32%
February 16, 2016	26%	0.89%
January 1, 2017	25%	1.49%
February 28, 2017	23%	1.43%

Schedule of Restricted Stock Activity

Below is a summary of our restricted stock activity for the year ended December 31, 2017.

Unvested Restricted Stock	Shares		Weighted-Average Grant Date Fair Value
Unvested, beginning of period	274,642		$	73.81
Granted (1)	120,853		108.65
Vested	(102,899	)	69.04
Cancelled or expired	(33,174	)	84.68
Unvested, end of period	259,422		$	90.54

(1) All restricted stock awards granted in 2017 are subject only to service conditions.