Quarterly report pursuant to Section 13 or 15(d)

Cash, Cash Equivalents and Investments - Summary of Available-for-sale Securities' Adjusted Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value by Significant Investment Category (Details)

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Cash, Cash Equivalents and Investments - Summary of Available-for-sale Securities' Adjusted Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value by Significant Investment Category (Details) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost $ 79,590 $ 99,165
Unrealized Gains 0 3
Unrealized Losses (10) (55)
Fair Value 79,580 99,113
Money market funds    
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost 61,524 55,752
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 61,524 55,752
Corporate debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost 18,066 43,413
Unrealized Gains 3
Unrealized Losses (10) (55)
Fair Value $ 18,056 $ 43,361