Equity - Summary of Restricted Stock Units (Detail) (USD $)
3 Months Ended
Mar. 31, 2015
Restricted Stock Units  
Number of Shares  
Beginning balance (in shares) 746,612
Granted (in shares) 418,584
Vested (in shares) (132,476)
Forfeited (in shares) (70,773)
Ending balance (in shares) 961,947
Weighted Average Fair Value  
Beginning balance (in USD per share) $ 31.40
Granted (in USD per share) $ 33.81
Vested (in USD per share) $ 29.68
Forfeited (in USD per share) $ 35.72
Ending balance (in USD per share) $ 32.35
Performance Shares  
Number of Shares  
Granted (in shares) 0
Maximum | Restricted Stock Units  
Number of Shares  
Vesting period 3 years