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Share-Based Compensation Information for Restricted Stock Units under Equity Incentive Plan (Detail) - Restricted stock units
12 Months Ended
Dec. 31, 2015
$ / shares
shares
Shares  
Nonvested, beginning of period (in shares) | shares 614,666
Granted (in shares) | shares 241,548
Vested (in shares) | shares (264,884)
Forfeited (in shares) | shares (19,292)
Nonvested, end of period (in shares) | shares 572,038
Weighted Average Grant Date Fair Value  
Nonvested, beginning of period (usd per share) | $ / shares $ 79.92
Granted (usd per share) | $ / shares 129.23
Vested (usd per share) | $ / shares 73.35
Forfeited (usd per share) | $ / shares 88.51
Nonvested, end of period (usd per share) | $ / shares $ 103.50