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Stock-Based Compensation Plans and Employee Benefits - Activities for Unvested Stock Option Awards (Detail) - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Options, Granted 154 633 557
Number of Options, Forfeited (731) (784) (472)
Weighted Average Exercise Price, Beginning balance $ 19.16 $ 20.29 $ 22.48
Weighted Average Exercise Price, Ending balance $ 17.11 $ 19.16 $ 20.29
Unvested stock option awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Options Outstanding, Beginning Balance 768    
Number of Options, Granted 154    
Number of options, Vested (394)    
Number of Options, Forfeited (146)    
Number of Options Outstanding, Ending Balance 382 768  
Weighted Average Exercise Price, Beginning balance $ 1.97    
Weighted-Average Grant-Date Fair Value, Granted 1.28    
Weighted-Average Grant-Date Fair Value, Vested 2.11    
Weighted-Average Grant-Date Fair Value, Forfeited 1.75    
Weighted Average Exercise Price, Ending balance $ 1.63 $ 1.97