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Stock Option Plans (Tables)
 12 Months Ended
Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award
The following table summarizes the Company’s stock option activity for the years ended December 31, 2011 and 2010:
 
 
December 31, 2011
 
December 31, 2010
 
Number
of Shares
 
Weighted
Average
Exercise
Price
 
Number
of Shares
 
Weighted
Average
Exercise
Price
Outstanding at beginning of period
1,581

 
$
11.68

 
1,491

 
$
10.39

Granted
150

 
36.75

 
250

 
17.27

Exercised
(724
)
 
9.72

 
(143
)
 
7.42

Expired or forfeited
(29
)
 
21.27

 
(17
)
 
17.35

Outstanding at end of period
978

 
$
16.69

 
1,581

 
$
11.68

Exercisable at end of year*
563

 
$
11.72

 
1,118

 
$
9.46

Participants at end of year
73

 
 
 
65

 
 
Available for future grants at end of year
533

 
 
 
795

 
 
 _______________
* Remaining contractual term of 7.0 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value
Weighted average grant date fair values of stock options and the assumptions used in estimating the fair values are as follows: 
 
2011
 
2010
 
2009
Weighted average grant date fair value
$
24.33

 
$
12.03

 
$
11.02

Expected term (years)
6.25

 
6.25

 
6.25

Risk-free interest rate
2.43
%
 
2.46
%
 
2.07
%
Expected volatility
72.47
%
 
77.84
%
 
74.87
%