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Shareholders' Equity (Tables)
 12 Months Ended
Dec. 31, 2019
Equity [Abstract]  
Summary of Activities in Common Stock
The following table details activity in our common stock:
 
Years Ended December 31,
 
2019
 
2018
 
2017
 
Shares
 
Amount
 
Shares
 
Amount
 
Shares
 
Amount
Stock option exercises
999

 
$
96,908

 
1,126

 
$
74,907

 
1,113

 
$
49,845

Purchases of common stock
(72
)
 
(14,289
)
 
(781
)
 
(150,050
)
 
(44
)
 
(6,613
)
Employee stock plan purchases
53

 
9,576

 
45

 
8,051

 
51

 
7,044

Restricted stock units vested, net of withheld shares upon award settlement
53

 
(5,361
)
 
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