Annual report pursuant to Section 13 and 15(d)

Stock-based Expense - Performance-Based Restricted Share Awards Activity (Detail)

v3.8.0.1
Stock-based Expense - Performance-Based Restricted Share Awards Activity (Detail) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Market Based Restricted Stock      
Number of Shares      
Beginning Balance (in shares) 1,564,160 1,015,095 520,000
Granted (in shares) 535,441 794,025 691,165
Vested (in shares) (1,407,133) (51,250)  
Forfeited/cancelled (in shares) (2,303) (193,710) (196,070)
Ending Balance (in shares) 690,165 1,564,160 1,015,095
Weighted-Average price      
Beginning of Period (in dollars per share) $ 12.73 $ 11.85 $ 11.26
Granted (in dollars per share) 28.18 13.58 11.59
Vested (in dollars per share) 13.69 12.52  
Forfeited/cancelled (in dollars per share) 13.34 11.61 9.39
Ending of Period (in dollars per share) $ 22.76 $ 12.73 $ 11.85
Performance Based Restricted Stock      
Number of Shares      
Beginning Balance (in shares) 0 20,000 0
Granted (in shares) 0   20,000
Forfeited/cancelled (in shares)   (20,000)  
Ending Balance (in shares) 0 0 20,000
Weighted-Average price      
Beginning of Period (in dollars per share) $ 0.00 $ 18.79 $ 0.00
Granted (in dollars per share) 0.00   18.79
Forfeited/cancelled (in dollars per share)   18.79  
Ending of Period (in dollars per share) $ 0.00 $ 0.00 $ 18.79