Net Income per Unit (Tables)
 3 Months Ended
Mar. 31, 2015
Net Income per Unit [Abstract]  
Net Income Per Unit
Diluted net income per unit is derived by adjusting net income for the assumed dilutive effect of compensatory options (“Net income – diluted”) and dividing by the diluted weighted average number of units outstanding for each period.

  
Three Months Ended March 31,
 
  
2015
  
2014
 
  
(in thousands, except per unit amounts)
 
     
Net income – basic
 $
45,585
  $
36,159
 
Additional allocation of equity in net income attributable to AB resulting from assumed dilutive effect of compensatory options
  
355
   
296
 
Net income – diluted
 $
45,940
  $
36,455
 
         
Weighted average units outstanding – basic
  
100,548
   
96,114
 
Dilutive effect of compensatory options
  
1,098
   
1,077
 
Weighted average units outstanding – diluted
  
101,646
   
97,191
 
         
Basic net income per unit
 $
0.45
  $
0.38
 
Diluted net income per unit
 $
0.45
  $
0.38