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Stock Option Plan - Additional Information (Detail) |  |  |  |  |  |  |  |  |  |  | 12 Months Ended |  |
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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 | Apr. 27, 2007 USD ($) person $ / shares shares | May. 01, 2006 USD ($) person $ / shares shares | Dec. 31, 2015 USD ($) $ / shares | Dec. 31, 2014 $ / shares | Dec. 31, 2013 $ / 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 |  |  |  |  |  |  |  |  |  |  | $ 51.07 | $ 47.03 | $ 44.42 |  |
Fair value stock option grant | $ |  |  |  |  |  |  |  |  |  |  | $ 10,822,000 |  |  |  |
the 1993 Plan | Stock Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized shares for a grant |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |
2006 Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of options (in usd per share) | $ / shares |  |  |  |  |  |  |  |  |  | $ 40.35 |  |  |  |  |
Fair value stock option grant | $ |  |  |  |  |  |  |  |  |  | $ 143,400 |  |  |  |  |
2006 Options | Director |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of individuals granted options | person |  |  |  |  |  |  |  |  |  | 12 |  |  |  |  |
2006 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 |  |  |  |  |
2006 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 |  |  |  |  |
2007 Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of options (in usd per share) | $ / shares |  |  |  |  |  |  |  |  | $ 54.17 |  |  |  |  |  |
Fair value stock option grant | $ |  |  |  |  |  |  |  |  | $ 1,500,000 |  |  |  |  |  |
2007 Options | Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of individuals granted options | person |  |  |  |  |  |  |  |  | 13 |  |  |  |  |  |
Options vested (in percent) |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |  |
Fair value stock option grant | $ |  |  |  |  |  |  |  |  | $ 1,300,000 |  |  |  |  |  |
2007 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 | $ |  |  |  |  |  |  |  |  | $ 285,300 |  |  |  |  |  |
2007 Options | Stock Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options granted to purchase stocks (in shares) |  |  |  |  |  |  |  |  | 165,000 |  |  |  |  |  |
2007 Options | Stock Options | Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option vesting period |  |  |  |  |  |  |  |  | 4 years |  |  |  |  |  |
2007 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) |  |  |  |  |  |  |  |  | 27,560 |  |  |  |  |  |
2007 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) |  |  |  |  |  |  |  |  | 137,440 |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |
Options vested (in percent) |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ |  |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |
Options vested (in percent) |  |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ |  |  |  | $ 1,400,000 |  |  |  |  |  |  |  |  |  |  |
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] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested (in percent) |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ |  |  | $ 1,300,000 |  |  |  |  |  |  |  |  |  |  |  |
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 | $ |  |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested (in percent) |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ |  | $ 1,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |
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 | $ | $ 1,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Options | Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of individuals granted options | person | 19 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested (in percent) | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ | $ 1,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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