Stock Option Plan - Additional Information (Detail)					12 Months Ended
	Dec. 31, 2019 USD ($) shares	May 03, 2019 USD ($) person $ / shares shares	May 11, 2018 USD ($) person $ / shares shares	May 05, 2017 USD ($) person $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 $ / shares	Dec. 31, 2017 $ / shares	Dec. 31, 2004 shares
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Deferred compensation (in shares)	114,408				6,822
Exercise price of options (in usd per share) | $ / shares					$ 55.71	$ 49.46	$ 59.41
Allocated share based compensation | $					$ 1,600,000
Future expense | $	$ 2,600,000				$ 2,600,000
Stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Expiration period								10 years
Stock options | Officer
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Option vesting period								4 years
Amended 2004 Plan | Stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Authorized shares for a grant (in shares)								3,400,000
2017 Options
Share-based Payment Arrangement, Option, 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 Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of individuals granted options | person				20
Options vested				25.00%
Fair value stock option grant | $				$ 1,200,000
2017 Options | Director
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of individuals granted options | person				11
Fair value stock option grant | $				$ 165,600
2017 Options | Stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)				232,500
2017 Options | Stock options | Officer
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Option vesting period				4 years
2017 Options | Incentive stock option
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)				21,492
2017 Options | Nonqualified stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)				211,008
2018 Options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares			$ 49.46
Fair value stock option grant | $			$ 1,400,000
2018 Options | Officer
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of individuals granted options | person			22
Options vested			25.00%
Fair value stock option grant | $			$ 1,200,000
2018 Options | Director
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of individuals granted options | person			11
Fair value stock option grant | $			$ 169,400
2018 Options | Stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)			245,000
2018 Options | Stock options | Officer
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Option vesting period			4 years
2018 Options | Incentive stock option
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)			25,914
2018 Options | Nonqualified stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)			219,086
2019 Options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price of options (in usd per share) | $ / shares		$ 55.71
Fair value stock option grant | $		$ 1,900,000
2019 Options | Officer
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of individuals granted options | person		23
Options vested		25.00%
Fair value stock option grant | $		$ 1,700,000
2019 Options | Director
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of individuals granted options | person		11
Fair value stock option grant | $		$ 226,600
2019 Options | Stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)		260,000
2019 Options | Stock options | Officer
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Option vesting period		4 years
2019 Options | Incentive stock option
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)		34,651
2019 Options | Nonqualified stock options
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options granted to purchase stocks (in shares)		225,349
Common Stock
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares)					7,058