Marketable Securities
 9 Months Ended
Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]  
Marketable Securities
Marketable Securities
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, 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 marketable securities designated as available-for-sale as of September 30, 2016:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
Corporate bonds
$
100,964

 
$
14

 
$
(126
)
 
$
100,852

Government securities
9,695

 
10

 
—

 
9,705

Commercial paper
8,187

 
—

 
—

 
8,187

Agency securities
7,255

 
3

 
—

 
7,258

Municipal bonds
4,050

 
—

 
(2
)
 
4,048

Certificates of deposit
1,248

 
—

 
—

 
1,248

Total marketable securities
$
131,399

 
$
27

 
$
(128
)
 
$
131,298


The following is a summary of amortized cost and estimated fair value of marketable securities as of September 30, 2016 by maturity:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
Due in one year or less
$
121,461

 
$
27

 
$
(94
)
 
$
121,394

Due after one year
9,938

 
—

 
(34
)
 
$
9,904

Total marketable securities
$
131,399

 
$
27

 
$
(128
)
 
$
131,298


The following is a summary of marketable securities designated as available-for-sale as of December 31, 2015:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
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


The following is a summary of amortized cost and estimated fair value of marketable securities as of December 31, 2015 by maturity:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Estimated
Fair Value
 
(in thousands)
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