Nonvested Share-Awards Activity (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Nonvested Stock Awards, shares  
Nonvested at beginning of period, shares 343
Awarded 81
Released (29)
Forfeited (11)
Nonvested at end of period, shares 384
Weighted Average Grant Date Fair Value  
Nonvested at beginning of period $ 27.99
Awarded $ 37.22
Released $ 34.78
Forfeited $ 24.14
Nonvested at end of period $ 29.57