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Cash Equivalents and Investments - Schedule of Available-for-Sale Securities Unrealized Loss Position (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]    
Available-for-sale securities, unrealized loss position, Less than 12 months, Fair Value $ 2,498 $ 17,498
Available-for-sale securities, unrealized loss position, Less than 12 months, Unrealized Loss   (11)
Available-for-sale securities, unrealized loss position, Greater than 12 months, Fair Value   2,993
Available-for-sale securities, unrealized loss position, Greater than 12 months, Unrealized Loss   (8)
Available-for-sale securities, unrealized loss position, Total, Fair Value 2,498 20,491
Available-for-sale securities, unrealized loss position, Total, Unrealized Loss   (19)
U.S. Government Securities    
Schedule Of Available For Sale Securities [Line Items]    
Available-for-sale securities, unrealized loss position, Less than 12 months, Fair Value   5,977
Available-for-sale securities, unrealized loss position, Less than 12 months, Unrealized Loss   (1)
Available-for-sale securities, unrealized loss position, Total, Fair Value   5,977
Available-for-sale securities, unrealized loss position, Total, Unrealized Loss   (1)
Corporate Notes    
Schedule Of Available For Sale Securities [Line Items]    
Available-for-sale securities, unrealized loss position, Less than 12 months, Fair Value 2,498 11,521
Available-for-sale securities, unrealized loss position, Less than 12 months, Unrealized Loss   (10)
Available-for-sale securities, unrealized loss position, Greater than 12 months, Fair Value   2,993
Available-for-sale securities, unrealized loss position, Greater than 12 months, Unrealized Loss   (8)
Available-for-sale securities, unrealized loss position, Total, Fair Value $ 2,498 14,514
Available-for-sale securities, unrealized loss position, Total, Unrealized Loss   $ (18)