Fully Vested Stock Options and Stock Options Expected to Vest (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Number of Shares    
Outstanding 2,995 2,649
Vested and expected to vest 2,887  
Exercisable 1,659  
Weighted Average Exercise Price    
Outstanding $ 33.53 $ 32.33
Vested and expected to vest $ 33.28  
Exercisable $ 30.80  
Weighted Average Remaining Contractual Term (In years)    
Outstanding 8 years 1 month 10 days  
Vested and expected to vest 8 years 26 days  
Exercisable 7 years 8 months 5 days  
Aggregate Intrinsic Values    
Outstanding $ 28,595  
Vested and expected to vest 28,242  
Exercisable $ 19,997