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Marketable Securities
 3 Months Ended
Mar. 31, 2016
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 March 31, 2016 and December 31, 2015:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
March 31, 2016
 
 
 
 
 
 
 
Corporate bonds
$
115,144

 
$
14

 
$
(90
)
 
$
115,068

Municipal bonds
13,130

 
—

 
(6
)
 
13,124

Government securities
11,693

 
12

 
(2
)
 
11,703

Commercial paper
7,473

 
—

 
—

 
7,473

Agency securities
7,267

 
—

 
(1
)
 
7,266

Certificates of deposit
2,244

 
—

 
—

 
2,244

Total marketable securities
$
156,951

 
$
26

 
$
(99
)
 
$
156,878

December 31, 2015
 
 
 
 
 
 
 
Corporate bonds
$
125,132

 
$
1

 
$
(304
)
 
$
124,829

Commercial paper
37,236

 
—

 
—

 
37,236

Municipal bonds
16,228

 
2

 
(6
)
 
16,224

Government securities
8,704

 
1

 
(17
)
 
8,688

Agency securities
7,273

 
—

 
(20
)
 
7,253

Certificates of deposit
2,244

 
—

 
—

 
2,244

Total marketable securities
$
196,817

 
$
4

 
$
(347
)
 
$
196,474


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 March 31, 2016 and December 31, 2015, 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 March 31, 2016 and December 31, 2015, by maturity:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
March 31, 2016
 
 
 
 
 
 
 
Due in one year or less
$
145,592

 
$
18

 
$
(89
)
 
$
145,521

Due after one year
11,359

 
8

 
(10
)
 
11,357

Total marketable securities
$
156,951

 
$
26

 
$
(99
)
 
$
156,878

December 31, 2015
 
 
 
 
 
 
 
Due in one year or less
$
164,147

 
$
2

 
$
(221
)
 
$
163,928

Due after one year
32,670

 
2

 
(126
)
 
32,546

Total marketable securities
$
196,817

 
$
4

 
$
(347
)
 
$
196,474