Annual report pursuant to Section 13 and 15(d)

Stock-based Expense - Summary of Time-Based Restricted Share Awards' Activity (Detail)

v3.8.0.1
Stock-based Expense - Summary of Time-Based Restricted Share Awards' Activity (Detail) - Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Number of Shares      
Beginning Balance (in shares) 1,633,501 1,068,706 1,624,519
Granted (in shares) 1,359,578 1,793,257 913,077
Vested (in shares) (953,749) (841,983) (1,077,102)
Forfeited/cancelled (in shares) (283,342) (386,479) (391,788)
Ending Balance (in shares) 1,755,988 1,633,501 1,068,706
Weighted-Average price      
Beginning of Period (in dollars per share) $ 20.78 $ 20.05 $ 20.01
Granted (in dollars per share) 36.25 20.79 19.84
Vested (in dollars per share) 23.73 20.14 19.78
Forfeited/cancelled (in dollars per share) 28.01 20.21 18.65
Ending of Period (in dollars per share) $ 30.05 $ 20.78 $ 20.05