Short-term Investments (Tables)
 12 Months Ended
Dec. 31, 2013
Short-term Investment [Abstract]  
Summary Of Investments In Available-For-Sale Securities [Table Text Block]
The following table summarizes the Company’s investments in available-for-sale securities as of December 31, 2013 and 2012 (in thousands):
 
December 31, 2013
 
 
 
Unrealized
 
 
 
Amortized Cost
 
Gains
 
Losses
 
Estimated Fair Value
Municipal bonds
$
146,047

 
$
56

 
$
(3
)
 
$
146,100

Commercial paper
31,597

 
—

 
—

 
31,597

Corporate bonds
7,873

 
2

 
—

 
7,875

U.S. government and agency securities
5,002

 
—

 
(7
)
 
4,995

 
$
190,519

 
$
58

 
$
(10
)
 
$
190,567


 
December 31, 2012
 
 
 
Unrealized
 
 
 
Amortized Cost
 
Gains
 
Losses
 
Estimated Fair Value
Municipal bonds
$
105,536

 
$
1

 
$
(22
)
 
$
105,515

Commercial paper
13,697

 
—

 
—

 
13,697

Corporate bonds
6,880

 
—

 
—

 
6,880

 
$
126,113

 
$
1

 
$
(22
)
 
$
126,092