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Marketable Securities (Tables)
 12 Months Ended
Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]  
Schedule of Marketable Securities
At December 31, 2018, marketable securities consisted of the following (in thousands):

 
Amortized Cost
 
Unrealized Gains
 
Unrealized Losses
 
Aggregate Fair Value
U.S. treasury securities
$
65,491

 
$
2

 
$
(4
)
 
$
65,489

Corporate bonds
19,708

 
15

 
(3
)
 
19,720

Commercial paper
11,894

 
—

 
—

 
11,894

     Short-term investments
$
97,093

 
$
17

 
$
(7
)
 
$
97,103

 
 
 
 
 
 
 
 
U.S. treasury securities
$
1,000

 
$
—

 
$
—

 
$
1,000

Commercial paper
6,635

 
—

 
—

 
6,635

Money market funds
15,223

 
 
 
 
 
15,223

    Cash equivalents
$
22,858

 
$
—

 
$
—

 
$
22,858

 
 
 
 
 
 
 
 
Total marketable securities
$
119,951

 
$
17

 
$
(7
)
 
$
119,961