Stock Option Plan - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended			1 Months Ended			1 Months Ended		1 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended			1 Months Ended			1 Months Ended						1 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 26, 2004 2004 Options	Apr. 26, 2004 2004 Options Officer	Apr. 26, 2004 2004 Options Director	May 06, 2005 2005 Options	May 06, 2005 2005 Options Officer Person	May 06, 2005 2005 Options Director Person	May 01, 2006 2006 Options	May 01, 2006 2006 Options Director Person	Apr. 27, 2007 2007 Options	Apr. 27, 2007 2007 Options Officer Person	Apr. 27, 2007 2007 Options Director Person	Apr. 25, 2008 2008 Options	Apr. 25, 2008 2008 Options Director Person	Apr. 24, 2009 2009 Options	Apr. 24, 2009 2009 Options Director Person	May 07, 2010 2010 Options	May 07, 2010 2010 Options Director Person	May 13, 2011 2011 Options	May 13, 2011 2011 Options Officer Person	May 13, 2011 2011 Options Director Person	May 04, 2012 2012 Options	May 04, 2012 2012 Options Officer Person	May 04, 2012 2012 Options Director Person	May 10, 2013 2013 Options Person	May 10, 2013 2013 Options Officer	May 10, 2013 2013 Options Director Person	Dec. 31, 1993 Stock Options the 1993 Plan	Dec. 31, 2004 Stock Options Amended 2004 Plan	Dec. 31, 2004 Stock Options Amended 2004 Plan Director	Apr. 26, 2004 Stock Options 2004 Options	Apr. 26, 2004 Stock Options 2004 Options Officer Person	Apr. 26, 2004 Stock Options 2004 Options Director Person	May 06, 2005 Stock Options 2005 Options	May 06, 2005 Stock Options 2005 Options Officer	May 01, 2006 Stock Options 2006 Options	Apr. 27, 2007 Stock Options 2007 Options	Apr. 27, 2007 Stock Options 2007 Options Officer	Apr. 25, 2008 Stock Options 2008 Options	Apr. 24, 2009 Stock Options 2009 Options	May 07, 2010 Stock Options 2010 Options	May 13, 2011 Stock Options 2011 Options	May 13, 2011 Stock Options 2011 Options Officer	May 04, 2012 Stock Options 2012 Options	May 04, 2012 Stock Options 2012 Options Officer	May 10, 2013 Stock Options 2013 Options	May 04, 2012 Stock Options 2013 Options Officer	Apr. 26, 2004 Incentive Stock Option 2004 Options	May 06, 2005 Incentive Stock Option 2005 Options	Apr. 27, 2007 Incentive Stock Option 2007 Options	May 13, 2011 Incentive Stock Option 2011 Options	May 04, 2012 Incentive Stock Option 2012 Options	May 10, 2013 Incentive Stock Option 2013 Options	Apr. 26, 2004 Nonqualified Stock Options 2004 Options	May 06, 2005 Nonqualified Stock Options 2005 Options	Apr. 27, 2007 Nonqualified Stock Options 2007 Options	May 13, 2011 Nonqualified Stock Options 2011 Options	May 04, 2012 Nonqualified Stock Options 2012 Options	May 10, 2013 Nonqualified Stock Options 2013 Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Authorized shares for a grant																														400,000	2,000,000	200,000
Options granted to purchase stocks (in shares)																																	152,500			162,500		30,000	165,000		30,000	32,500	32,500	195,000		277,500		237,500		27,500	35,500	27,560	65,300	26,157	35,592	125,000	127,000	137,440	129,700	251,343	201,908
Number of individuals granted options								12	12		12		13	12		12		13		13		15	13		15	14	15		14					11	12
Plan expiration date				Apr. 25, 2014			May 05, 2015			Apr. 30, 2016		Apr. 26, 2017			Apr. 24, 2018		Apr. 23, 2019		May 06, 2020		May 12, 2021			May 03, 2022			May 10, 2023
Options vested (in percent)					25.00%			25.00%					25.00%									25.00%			25.00%
Option vesting period																																		4 years			4 years			4 years					4 years		4 years		4 years
Exercise price of options (in usd per share)	$ 44.42	$ 39.29	$ 41.82	$ 25.78			$ 33.22			$ 40.35		$ 54.17			$ 50.15		$ 32.68		$ 38.76		$ 41.82			$ 39.29			$ 44.42
Fair value stock option grant	$ 8,075,838			$ 359,375	$ 292,775	$ 66,600	$ 484,500	$ 413,400	$ 71,100	$ 143,400		$ 1,500,000	$ 1,300,000	$ 285,300	$ 254,700		$ 222,950		$ 287,950		$ 1,600,000	$ 1,300,000	$ 297,375	$ 1,700,000	$ 1,400,000	$ 244,388	$ 1,500,000	$ 1,300,000	$ 300,000
Intrinsic value of options exercised	600,000	1,600,000	700,000
Intrinsic value of options outstanding	4,500,000
Intrinsic value of options exercisable	$ 2,800,000
Closing share price	$ 47.73
Weighted average remaining contractual life of the Company's exercisable options	5 years 1 month 1 day
Weighted average remaining contractual life of the Company's outstanding options	6 years 9 months 4 days