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Marketable Securities
 3 Months Ended
Mar. 31, 2016
Investments, Debt and Equity Securities [Abstract]  
Marketable Securities [Text Block]
Marketable Securities
The amortized cost, gross unrealized holding gains, gross unrealized holding losses and estimated fair value of available-for-sale investments by type of security at March 31, 2016 and December 31, 2015 were as follows:
 
 
March 31, 2016
 
 
Amortized Cost Basis
 
Gross Unrealized Holding Gains
 
Gross Unrealized Holding Losses
 
Aggregate Fair Value
Commercial paper
 
$
3,999

 
$
—

 
$
—

 
$
3,999

Corporate bonds
 
136,009

 
553

 
(3
)
 
136,559

Municipal bonds
 
50,470

 
43

 
(2
)
 
50,511

Other government-related obligations:
 
 
 
 
 
 
 
 
U.S.
 
13,643

 
43

 
(27
)
 
13,659

Foreign
 
141,593

 
244

 
(19
)
 
141,818

 
 
$
345,714

 
$
883

 
$
(51
)
 
$
346,546


 
 
December 31, 2015
 
 
Amortized Cost Basis
 
Gross Unrealized Holding Gains
 
Gross Unrealized Holding Losses
 
Aggregate Fair Value
Commercial paper
 
$
254,396

 
$
—

 
$
—

 
$
254,396

Corporate bonds
 
133,062

 
23

 
(336
)
 
132,749

Municipal bonds
 
87,173

 
1

 
(63
)
 
87,111

Other government-related obligations:
 
 
 
 
 
 
 
 
U.S.
 
25,244

 
—

 
(94
)
 
25,150

Foreign
 
163,403

 
—

 
(504
)
 
162,899

Bank certificates of deposit
 
27,000

 
—

 
—

 
27,000

 
 
$
690,278

 
$
24

 
$
(997
)
 
$
689,305



The aggregate fair value of available-for-sale securities in an unrealized loss position as of March 31, 2016 and December 31, 2015 was $62,496 and $293,947, respectively. Investments that have been in a continuous unrealized loss position for more than 12 months were not material. As of March 31, 2016, we believe that the cost basis of our available-for-sale investments is recoverable.
The fair values of available-for-sale securities by classification in the condensed consolidated balance sheet were as follows:
 
March 31, 2016
 
December 31, 2015
Cash and cash equivalents
$
40,999

 
$
323,218

Marketable securities
305,547

 
366,087

 
$
346,546

 
$
689,305



The fair values of available-for-sale debt securities at March 31, 2016, by contractual maturity, are summarized as follows:
 
March 31, 2016
Due in one year or less
$
140,145

Due after one year through three years
206,401

 
$
346,546



As of March 31, 2016 and December 31, 2015, the fair value of our trading securities was $11,807 and $8,817, respectively.
We utilize the specific identification method in computing realized gains and losses. Realized gains and losses on our available-for-sale and trading securities were not material for the three months ended March 31, 2016.