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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2012
Stock-Based Compensation [Abstract]  
Weighted average assumptions used to determine fair value for stock awards
      The fair value for stock awards was estimated at the date of grant using the Black-Scholes option valuation model with the following weighted average assumptions for the years ended December 31, 2012, 2011 and 2010:

 
2012
 
2011
 
2010
Expected life (years)                                                                      
 
6.9
 
 
 
6.3
 
 
 
6.3
 
Interest rate                                                                      
 
1.36
%
 
 
2.46
%
 
 
2.92
%
Volatility                                                                      
 
31.26
%
 
 
30.93
%
 
 
28.80
%
Expected dividend yield                                                                      
 
0.31
%
 
 
0.31
%
 
 
0.41
%
Summary of stock option activity
     The following table summarizes stock option activity for the year ended December 31, 2012:

 
 
Shares
 
 
 
 
Weighted Average Exercise Price Per Share
 
Weighted Average Remaining Contractual Life (Years)
 
 
Aggregate Intrinsic
         Value       
  (in thousands)
Balance December 31, 2011  
 
1,573,974
 
 
 
$
27.10
 
 
 
 
 
Granted  
 
222,250
 
 
 
 
32.04
 
 
 
 
 
Exercised  
 
(330,158
)
 
 
 
25.15
 
 
 
 
 
Canceled  
 
(70,546
)
 
 
 
27.76
 
 
 
 
 
Balance December 31, 2012  
 
1,395,520
 
 
 
$
28.31
 
5.93
 
$
16,201
 
 
 
 
 
 
 
 
 
 
 
 
 
Exercisable, December 31, 2012  
 
1,068,434
 
 
 
$
27.44
 
5.11
 
$
13,337
Non-vested stock option activity
     Non-vested stock option activity for the year ended December 31, 2012 is as follows:
 
 
 
Shares
 
 
Weighted Average Exercise Price Per Share
 
Non-vested options outstanding at December 31, 2011
 
454,634
 
$
27.14
 
Options granted                                                                                                  
 
222,250
 
 
32.04
 
Options vested                                                                                                  
 
(311,152
)
 
25.98
 
Options forfeited …
 
(38,646
)
 
30.63
 
Non-vested options outstanding at December 31, 2012  
 
327,086
 
$
31.17
 
Summary of outstanding options by exercise price
     The following table summarizes additional information concerning options outstanding at December 31, 2012:

Options Outstanding
 
Options Exercisable
Range of
 Exercise Prices
 
Number Outstanding at 12/31/12
 
Weighted Average Remaining Contractual Term (Years)
 
Weighted Average Exercise Price
 
Number Exercisable
at 12/31/12
 
Weighted Average Exercise Price
$
19.855
-
$
24.753
 
413,026
 
3.5
 
$
22.14
 
376,530
 
$
21.90
$
26.257
-
$
29.665
 
153,718
 
2.1
 
$
27.08
 
148,706
 
$
27.08
$
30.097
-
$
34.657
 
828,776
 
6.3
 
$
31.61
 
543,198
 
$
31.37
$
19.855
-
$
34.657
 
1,395,520
 
4.0
 
$
28.31
 
1,068,434
 
$
27.44
Summary of restricted stock activity
     The following table summarizes the restricted stock activity for the Plan:

 
 
 
 
Shares
 
 
 
Weighted Average Grant Date Fair Value
 
Unvested balance at December 31, 2011  
 
 
 
252,024
 
 
$
27.21
 
Granted  
 
 
 
123,446
 
 
$
32.04
 
Vested  
 
 
 
(102,424
)
 
$
25.90
 
Canceled  
 
 
 
(89,386
)
 
$
27.08
 
Unvested balance at December 31, 2012  
 
 
 
183,660
 
 
$
31.25