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Employee Bargaining Agreements and Benefit Plans - Assumption Rates Used for Net Periodic Benefit Costs (Detail)
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]      
Discount rate:     4.40%
Expected return on assets:   5.50% 5.50%
Maximum [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate: 3.90% 4.40%  
Expected return on assets: 5.50%    
Minimum [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate: 3.10% 3.90%  
Expected return on assets: 2.13%