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Employee Retirement and Postretirement Benefits - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Employee Benefit Plans [Line Items]        
Stock options, shares granted     1,992,595  
Stock options, shares exercised     48,662  
Stock options, shares forfeited     315,140  
Stock options, shares expired     265,024  
Employee Contribution     100.00%  
Percentage of employees contribution matched by the company     4.00%  
Employer Contribution $ 1.2 $ 1.1 $ 4.0 $ 3.1
Employee Stock Purchase Plan [Member]        
Employee Benefit Plans [Line Items]        
Common stock, shares issued under ESPP     117,471  
Market Condition [Member]        
Employee Benefit Plans [Line Items]        
Stock options, shares granted     527,850  
Stock options, shares forfeited     33,620  
Share units granted     228,840  
Share units forfeited     27,940  
Restricted Stock Units (RSUs) [Member]        
Employee Benefit Plans [Line Items]        
Share units granted     875,166  
Share units vested     368,506  
Share units forfeited     196,167  
Restricted Stock [Member]        
Employee Benefit Plans [Line Items]        
Share units granted     92,910  
Share units vested     98,988  
Deferred Stock Units [Member]        
Employee Benefit Plans [Line Items]        
Share units granted     60,972  
Share units released     0