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Employee Retirement and Postretirement Benefits - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Employee Benefit Plans [Line Items]    
Stock options, shares granted 2,239,417  
Stock options, shares exercised 253,653  
Stock options, shares expired 288,250  
Employee Contribution 100.00%  
Percentage of employees contribution matched by the company 4.00%  
Employer Contribution $ 1.2 $ 1.6
Employee Stock Purchase Plan [Member]    
Employee Benefit Plans [Line Items]    
Common stock, shares issued under ESPP 55,812  
Market Condition [Member]    
Employee Benefit Plans [Line Items]    
Stock options, shares granted 633,012  
Stock options, shares forfeited 207,527  
Share units granted 205,993  
Share units forfeited 33,692  
Restricted Stock Units (RSUs) [Member]    
Employee Benefit Plans [Line Items]    
Share units granted 696,260  
Share units vested 148,302  
Share units forfeited 58,045  
Restricted Stock [Member]    
Employee Benefit Plans [Line Items]    
Share units vested 14,271  
Deferred Stock Units [Member]    
Employee Benefit Plans [Line Items]    
Share units granted 25,331  
Share units vested 25,331