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Note Net income (loss) per common share - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]    
Accelerated Share Repurchases Final Price Paid Per Share $ 40.6  
Stock Repurchase Program Authorized Amount $ 75  
Total Common Shares Repurchased Accelerated Share Repurchase Agreements 1,847,372  
Employee Stock Option    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 0 0