Stock Option Plan - Additional Information (Detail)											12 Months Ended
	May 05, 2017 USD ($) person $ / shares shares	May 06, 2016 USD ($) person $ / shares shares	May 08, 2015 USD ($) person $ / shares shares	May 09, 2014 USD ($) person $ / shares shares	May 10, 2013 USD ($) person $ / shares shares	May 04, 2012 USD ($) person $ / shares shares	May 13, 2011 USD ($) person $ / shares shares	May 07, 2010 USD ($) person $ / shares shares	Apr. 24, 2009 USD ($) person $ / shares shares	Apr. 25, 2008 USD ($) person $ / shares shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 $ / shares	Dec. 31, 2015 $ / shares	Dec. 31, 2004 shares	Dec. 31, 1993 shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares											$ 59.41	$ 57.74	$ 51.07
Fair value stock option grant | $											$ 11,831,000
the 1993 Plan | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Authorized shares for a grant (in shares)															400,000
Amended 2004 Plan | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Authorized shares for a grant (in shares)														2,000,000
Amended 2004 Plan | Stock options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Authorized shares for a grant (in shares)														200,000
2008 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares										$ 50.15
Fair value stock option grant | $										$ 254,700
2008 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person										12
2008 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)										0
2008 Options | Stock options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)										30,000
2009 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares									$ 32.68
Fair value stock option grant | $									$ 222,950
2009 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person									13
2009 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)									0
2009 Options | Stock options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)									32,500
2010 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares								$ 38.76
Fair value stock option grant | $								$ 287,950
2010 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person								13
2010 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)								0
2010 Options | Stock options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)								32,500
2011 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares							$ 41.82
Fair value stock option grant | $							$ 1,600,000
2011 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person							15
Fair value stock option grant | $							$ 1,300,000
Options vested							25.00%
2011 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person							13
Fair value stock option grant | $							$ 297,375
2011 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)							195,000
2011 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period							4 years
2011 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)							65,300
2011 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)							129,700
2012 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares						$ 39.29
Fair value stock option grant | $						$ 1,700,000
2012 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person						15
Fair value stock option grant | $						$ 1,400,000
Options vested						25.00%
2012 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person						14
Fair value stock option grant | $						$ 257,250
2012 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)						277,500
2012 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period						4 years
2012 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)						26,157
2012 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)						251,343
2013 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person					15
Exercise price of options (in usd per share) | $ / shares					$ 44.42
Fair value stock option grant | $					$ 1,500,000
2013 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair value stock option grant | $					$ 1,200,000
Options vested					25.00%
2013 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person					14
Fair value stock option grant | $					$ 278,250
2013 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)					237,500
2013 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period					4 years
2013 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)					35,592
2013 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)					201,908
2014 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares				$ 47.03
Fair value stock option grant | $				$ 1,300,000
2014 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person				18
Fair value stock option grant | $				$ 1,200,000
Options vested				25.00%
2014 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person				12
Fair value stock option grant | $				$ 109,500
2014 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)				200,000
2014 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period				4 years
2014 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)				29,300
2014 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)				170,700
2015 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares			$ 51.07
Fair value stock option grant | $			$ 1,570,000
2015 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person			19
Fair value stock option grant | $			$ 1,440,000
Options vested			25.00%
2015 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person			14
Fair value stock option grant | $			$ 125,300
2015 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)			225,000
2015 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period			4 years
2015 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)			33,690
2015 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)			191,310
2016 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares		$ 57.74
Fair value stock option grant | $		$ 1,200,000
2016 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person		19
Fair value stock option grant | $		$ 1,000,000
Options vested		25.00%
2016 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person		13
Fair value stock option grant | $		$ 151,125
2016 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)		226,500
2016 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period		4 years
2016 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)		24,248
2016 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)		202,252
2017 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares	$ 59.41
Fair value stock option grant | $	$ 1,400,000
2017 Options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person	20
Fair value stock option grant | $	$ 1,200,000
Options vested	25.00%
2017 Options | Director
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of individuals granted options | person	11
Fair value stock option grant | $	$ 165,550
2017 Options | Stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)	232,500
2017 Options | Stock options | Officer
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option vesting period	4 years
2017 Options | Incentive stock option
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)	21,492
2017 Options | Nonqualified stock options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)	211,008