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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, 2016
$ / shares
shares
Shares  
Nonvested, beginning of period (in shares) | shares 572,038
Granted (in shares) | shares 361,646
Vested (in shares) | shares (220,476)
Forfeited (in shares) | shares (42,239)
Nonvested, end of period (in shares) | shares 670,969
Weighted Average Grant Date Fair Value  
Nonvested, beginning of period (usd per share) | $ / shares $ 103.50
Granted (usd per share) | $ / shares 100.35
Vested (usd per share) | $ / shares 88.24
Forfeited (usd per share) | $ / shares 106.38
Nonvested, end of period (usd per share) | $ / shares $ 106.64