Employees, Retirement and Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2013

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

Schedule of Nonvested Restricted Stock Units Activity

A summary of restricted unit activity and changes during the six months ended June 30, 2013 is presented below:

Restricted Units	Units	Weighted- Average Grant-Date Fair Value
Outstanding at January 1, 2013 (nonvested)	58,472	$	31.21
Granted	37,815	41.18
Vesting and transfer of full ownership to recipients	—	—
Outstanding at June 30, 2013 (nonvested)	96,287	$	35.08

Schedule of Nonvested Performance-based Units Activity

A summary of performance unit activity and changes during the six months ended June 30, 2013 is presented below:

Performance Units	Units
Outstanding at January 1, 2013 (nonvested)	54,498
Granted	32,888
Vesting and transfer of common units to recipients	(25,124	)
Outstanding at June 30, 2013 (nonvested)	62,262