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Share-Based Compensation - Performance Share Units - Narrative (Detail) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation $ 3.5 $ 3.5    
Performance share units        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Equity instruments other than options, percentage of expected payout     100.00% 100.00%
Granted, Shares     418,000 319,000
Share-based compensation 1.1 $ 0.7    
Unrecognized share-based compensation cost $ 5.7      
Unrecognized compensation expense, weighted-average period of recognition 1 year 6 months