GILEAD SCIENCES INC | 2013 | FY | 3

The following table summarizes our available-for-sale debt securities that were in a continuous unrealized loss position, but were not deemed to be other-than-temporarily impaired (in thousands):
 
 
Less Than 12 Months
 
12 Months or Greater
 
Total
 
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
December 31, 2013
 
 
 
 
 
 
 
 
 
 
 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
 
 
U.S. treasury securities
 
$
(28
)
 
$
24,562

 
$
—

 
$
—

 
$
(28
)
 
$
24,562

U.S. government agencies securities
 
(17
)
 
10,858

 
—

 
—

 
(17
)
 
10,858

Municipal debt securities
 
—

 
—

 
—

 
—

 
—

 
—

Corporate debt securities
 
(102
)
 
37,076

 
—

 
1,505

 
(102
)
 
38,581

Residential mortgage and asset-backed securities
 
(38
)
 
19,563

 
(27
)
 
6,731

 
(65
)
 
26,294

Total
 
$
(185
)
 
$
92,059

 
$
(27
)
 
$
8,236

 
$
(212
)
 
$
100,295

 
 
 

 
 

 
 

 
 

 
 

 
 

December 31, 2012
 
 

 
 

 
 

 
 

 
 

 
 

Debt securities:
 
 

 
 

 
 

 
 

 
 

 
 

U.S. treasury securities
 
$
—

 
$
—

 
$
—

 
$
—

 
$
—

 
$
—

U.S. government agencies securities
 
(29
)
 
26,306

 
—

 
—

 
(29
)
 
26,306

Municipal debt securities
 
(7
)
 
3,993

 
—

 
—

 
(7
)
 
3,993

Corporate debt securities
 
(84
)
 
72,722

 
—

 
—

 
(84
)
 
72,722

Residential mortgage and asset-backed securities
 
(141
)
 
36,415

 
—

 
—

 
(141
)
 
36,415

Total
 
$
(261
)
 
$
139,436

 
$
—

 
$
—

 
$
(261
)
 
$
139,436

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