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Stockholders' Equity - Summary of Activity for Outstanding PSUs awards (Detail) - PSU Awards [Member]
$ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Outstanding at December 31, 2014 1,346,375
Granted 224,760 [1]
Converted (432,574)
Forfeited or expired (57,116)
Outstanding at December 31, 2015 1,081,445
Fully vested at December 31, 2015 531,440
Aggregate Intrinsic Value | $ $ 19.6 [2]
Fully vested at December 31, 2015 | $ $ 47.4 [2]
[1] This represents the target number of performance units granted. Actual number of PSUs earned, if any, is dependent upon performance and may range from 0% to 200% percent of the target.
[2] These amounts represent actual number of PSUs earned and vested at December 31, 2014 which were issued in February 2015.