Annual report pursuant to Section 13 and 15(d)

Composition of Certain Financial Statement Captions - Schedule of cash, cash equivalents and investments (Details)

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Composition of Certain Financial Statement Captions - Schedule of cash, cash equivalents and investments (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Cash, Cash Equivalents and Investments        
Total cash and cash equivalents $ 499,597 $ 199,944 $ 334,667 $ 175,957
Total short-term investments 1,250 37,109    
Total long-term investments 0 6,252    
Cash, cash equivalents and investments 500,847 243,305    
Cash        
Cash, Cash Equivalents and Investments        
Total cash and cash equivalents 146,294 144,192    
Money market funds        
Cash, Cash Equivalents and Investments        
Total cash and cash equivalents 353,303 55,752    
Corporate debt securities        
Cash, Cash Equivalents and Investments        
Total short-term investments 1,250 37,109    
Total long-term investments $ 0 $ 6,252