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Marketable Securities
 9 Months Ended
Sep. 30, 2015
Investments, Debt and Equity Securities [Abstract]  
Marketable Securities
Marketable Securities
The following is a summary of marketable securities designated as available-for-sale as of September 30, 2015 and December 31, 2014:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
September 30, 2015
 
 
 
 
 
 
 
Corporate bonds
$
131,740

 
$
6

 
$
(116
)
 
$
131,630

Municipal bonds
17,957

 
14

 
(1
)
 
17,970

Commercial paper
36,118

 
—

 
—

 
36,118

Agency securities
7,279

 
7

 
—

 
7,286

Certificates of deposit
2,492

 
—

 
—

 
2,492

Government securities
1,199

 
2

 
—

 
1,201

Total marketable securities
$
196,785

 
$
29

 
$
(117
)
 
$
196,697

December 31, 2014
 
 
 
 
 
 
 
Corporate bonds
$
99,592

 
$
1

 
$
(119
)
 
$
99,474

Municipal bonds
18,146

 
1

 
(10
)
 
18,137

Commercial paper
9,196

 
—

 
—

 
9,196

Certificates of deposit
498

 
—

 
—

 
498

Total marketable securities
$
127,432

 
$
2

 
$
(129
)
 
$
127,305


We classify all marketable securities as current regardless of contractual maturity dates because we consider such investments to represent cash available for current operations.
As of September 30, 2015 and December 31, 2014, we did not consider any of our marketable securities to be other-than-temporarily impaired.  When evaluating our investments for other-than-temporary impairment, we review factors such as the length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer, our ability and intent to hold the security, and whether it is more likely than not that we will be required to sell the investment before recovery of its cost basis.
The following is a summary of amortized cost and estimated fair value of marketable securities as of September 30, 2015 and December 31, 2014, by maturity:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
September 30, 2015
 
 
 
 
 
 
 
Due in one year or less
$
147,745

 
$
13

 
$
(75
)
 
$
147,683

Due after one year
49,040

 
16

 
(42
)
 
49,014

Total marketable securities
$
196,785

 
$
29

 
$
(117
)
 
$
196,697

December 31, 2014
 
 
 
 
 
 
 
Due in one year or less
$
127,029

 
$
2

 
$
(129
)
 
$
126,902

Due after one year
403

 
—

 
—

 
403

Total marketable securities
$
127,432

 
$
2

 
$
(129
)
 
$
127,305