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Employee Benefits and Incentive Plans - Summary of Executive Management Rollover Options (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Options, Exercised (413,008) (112,216) (218,872)
Executive Management Rollover Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options Available for Grant, Beginning Balance 0    
Option Available for Grant, Exercised 0    
Options Available for Grant, Ending Balance 0 0  
Number of Options, Beginning Balance 12,416    
Number of Options, Exercised (12,416)    
Number of Options, Ending Balance   12,416  
Weighted Average Exercise Price, Beginning Balance $ 5.47    
Weighted Average Exercise Price, Exercised $ 5.47    
Weighted Average Exercise Price, Ending Balance   $ 5.47