Income per Unit

The following is a summary of basic and diluted income per unit (in thousands, except unit and per unit amounts):



	Year Ended December 31,
	2015		2014		2013
Net income available to common unitholders	$	220,343	$	135,485	$	276,949
Weighted average units outstanding—basic	140,905,897		136,122,661		130,462,534
Potentially dilutive common units:
Stock options	20,424		30,434		61,375
Unvested incentive units	95,746		90,449		125,132
Market performance-based awards	501,645		147,305		—
Weighted average units outstanding—diluted	141,523,712		136,390,849		130,649,041
Income per unit:
Basic	$	1.56	$	1.00	$	2.12
Diluted	$	1.55	$	0.99	$	2.12

We have excluded the following potentially dilutive securities in the calculations above as they would be antidilutive or not dilutive:



	Year Ended December 31,
	2015	2014	2013
Potentially dilutive 2029 Debentures	—	1,957,963	6,649,510
Potentially dilutive Series D Cumulative Convertible Preferred Units	—	—	470,748
Potentially dilutive Series E Cumulative Redeemable Preferred Units	4,301,438	4,956,175	5,176,886
Potentially dilutive Series F Cumulative Redeemable Preferred Units	2,727,962	3,143,195	3,283,169
Potentially dilutive Series G Cumulative Redeemable Preferred Units	3,730,042	4,297,805	3,898,376
Potentially dilutive Series H Cumulative Redeemable Preferred Units	5,465,987	4,320,495	—
Potentially dilutive Series I Cumulative Redeemable Preferred Units	1,235,063	—	—
	17,460,492	18,675,633	19,478,689