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Stock Option Plan - Additional Information (Detail) |  |  |  |  |  |  |  |  |  |  | 12 Months Ended |  |
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May 11, 2018 USD ($) person $ / shares shares | 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 | Dec. 31, 2018 USD ($) $ / shares | Dec. 31, 2017 $ / shares | Dec. 31, 2016 $ / 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 |  |  |  |  |  |  |  |  |  |  | $ 49.46 | $ 59.41 | $ 57.74 |  |
Fair value stock option grant | $ |  |  |  |  |  |  |  |  |  |  | $ 13,060,000 |  |  |  |
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 |
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 | $ |  |  | $ 151,100 |  |  |  |  |  |  |  |  |  |  |  |
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 | $ |  | $ 165,600 |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |
2018 Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, 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 Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of individuals granted options | person | 22 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ | $ 1,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 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 | $ | $ 169,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 Options | Stock options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options granted to purchase stocks (in shares) | 245,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 Options | Stock options | Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option vesting period | 4 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 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) | 25,914 |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 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) | 219,086 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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