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Share-Based Compensation and Benefit Plans (Tables)
3 Months Ended
Mar. 31, 2016
Restricted stock [Member]  
Share-Based Compensation and Benefit Plans  
Summary of activity of share-based compensation
 
For the Three Months Ended 
 March 31,
 
2016
 
2015
Compensation expense for shares issued under the ESPP
$
523

 
$
489

Income tax benefit from compensation expense related to shares issued under the ESPP
195

 
181

Compensation expense for restricted shares awarded
319

 
404

Income tax benefit from compensation expense related to restricted awards
$
119

 
$
149


Stock option [Member]  
Share-Based Compensation and Benefit Plans  
Summary of stock options
 
Shares
 
Weighted-Average
Exercise Price
Outstanding at December 31, 2015
3,308

 
$
80.86

Granted
192

 
263.18

Exercised
(206
)
 
63.65

Forfeited
(14
)
 
112.13

Outstanding at March 31, 2016
3,280

 
$
92.50

Exercisable at March 31, 2016
2,357

 
$
58.75


Black-Scholes option pricing model
 
For the Three Months Ended 
 March 31,
 
2016
 
2015
Risk free interest rate
1.59
%
 
1.57
%
Expected life
5.9 Years

 
6.1 Years

Expected volatility
22.4
%
 
22.4
%
Expected dividend yield
%
 
%

Summary of activity of share-based compensation
 
For the Three Months Ended 
 March 31,
 
2016
 
2015
Compensation expense for stock options awarded
$
4,336

 
$
4,997

Income tax benefit from compensation expense related to stock options
1,620

 
1,847

Weighted-average grant-date fair value of options awarded
$
66.27

 
$
51.57