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Marketable Securities (Tables)
3 Months Ended
Mar. 31, 2017
Investments Debt And Equity Securities [Abstract]  
Summary of Available for Sale Securities Held

The following table summarizes the available-for-sale securities held at March 31, 2017 and December 31, 2016 (in thousands):

 

Description

 

Amortized Cost

 

 

Unrealized Gains

 

 

Unrealized Losses

 

 

Fair Value

 

March 31, 2017

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

U.S. government agency securities and treasuries

 

$

580,667

 

 

$

11

 

 

$

(656

)

 

$

580,022

 

Certificates of deposit

 

 

3,840

 

 

 

6

 

 

 

 

 

 

3,846

 

Total

 

$

584,507

 

 

$

17

 

 

$

(656

)

 

$

583,868

 

December 31, 2016

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

U.S. government agency securities and treasuries

 

$

600,001

 

 

$

34

 

 

$

(575

)

 

$

599,460

 

Certificates of deposit

 

 

6,480

 

 

 

6

 

 

 

(3

)

 

 

6,483

 

Total

 

$

606,481

 

 

$

40

 

 

$

(578

)

 

$

605,943