Annual report pursuant to Section 13 and 15(d)

Composition of Certain Financial Statement Captions - 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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Composition of Certain Financial Statement Captions - Summary of available-for-sale securities' adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category (Details)
$ in Thousands
Dec. 31, 2016
USD ($)
Schedule of Available-for-sale Securities [Line Items]  
Adjusted Cost $ 99,165
Unrealized Gains 3
Unrealized Losses (55)
Fair Value 99,113
Money market funds  
Schedule of Available-for-sale Securities [Line Items]  
Adjusted Cost 55,752
Unrealized Gains 0
Unrealized Losses 0
Fair Value 55,752
Corporate debt securities  
Schedule of Available-for-sale Securities [Line Items]  
Adjusted Cost 43,413
Unrealized Gains 3
Unrealized Losses (55)
Fair Value $ 43,361