Units Outstanding (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2013

Dec. 31, 2012

Units Outstanding [Abstract]

Changes in units outstanding

Changes in units outstanding during the three-month and nine-month periods ended September 30, 2013 were as follows:

	Three Months Ended September 30, 2013			Nine Months Ended September 30, 2013
Outstanding as of beginning of period		278,374,893			277,600,901
Options exercised		33,903			812,642
Units issued		—			—
Units retired		(13,936,468	)		(13,941,215	)
Outstanding as of September 30, 2013		264,472,328			264,472,328

Changes in units outstanding for the years ended December 31, 2012 and 2011 were as follows:

	2012			2011
Outstanding as of January 1,		277,847,588			278,115,232
Options exercised		—			86,543
Units issued		—			—
Units retired		(246,687	)		(354,187	)
Units forfeited		—			—
Outstanding as of December 31,		277,600,901			277,847,588