Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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Unit-Based Compensation (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 0.4	$ 0.3	$ 0.8	$ 0.6
Restricted unit awards unamortized grant date fair value	4.0		4.0
Common Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common unit awards authorized	1,800,000		1,800,000
Restricted Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested units, December 31, 2012			271,000
Restricted unit awards outstanding	239,281		239,281
Restricted unit awards unamortized grant date fair value	$ 4.0		$ 4.0
Weighted average amortization period of grant date fair value, years			3 years