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Stockholders' Equity - Summary of Activity for Outstanding Three-year PSU Awards (Detail) - PSU Awards [Member]
$ in Millions
12 Months Ended
Dec. 31, 2016
USD ($)
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Outstanding at December 31, 2015 1,081,445
Granted 290,146 [1]
Converted (537,009)
Forfeited or expired (6,870)
Outstanding at December 31, 2016 827,712
Fully vested at December 31, 2016 374,267
Aggregate Intrinsic Value | $ $ 46.6 [2]
Fully vested at December 31, 2016 | $ $ 17.0 [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] The aggregate intrinsic value is based on the actual number of PSUs earned and vested at December 31, 2015 which were issued in February 2016.