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Cash Equivalents and Investments - Schedule of Fair Value of Short-term and Long-term Marketable Securities Classified by Maturity (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Marketable Securities [Abstract]    
Due within one year $ 54,120 $ 73,411
Total available-for-sale marketable debt securities $ 54,120 $ 73,411