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Cash, Cash Equivalents and Investments - Investment Category and Length (Details)
 12 Months Ended
Dec. 31, 2016
USD ($)
company
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]      
Fair value, in loss position less than twelve months $ 10,248,000 $ 11,375,000  
Gross unrealized loss, in loss position less than twelve months (55,000) (67,000)  
Fair value, in loss position greater than twelve months 4,595,000 5,390,000  
Gross unrealized loss, in loss position greater than twelve months (12,000) (9,000)  
Fair value, total in loss position 14,843,000 16,765,000  
Gross unrealized loss, total in loss position (67,000) (76,000)  
Minority Investments      
Investments in privately-held companies $ 6,599,000 7,948,000  
Equity method investments | company 7    
Cost method investments $ 0    
Certificates of Deposit [Member]      
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]      
Fair value, in loss position less than twelve months 5,211,000 4,509,000  
Gross unrealized loss, in loss position less than twelve months (20,000) (11,000)  
Fair value, in loss position greater than twelve months 1,200,000 3,543,000  
Gross unrealized loss, in loss position greater than twelve months   (2,000)  
Fair value, total in loss position 6,411,000 8,052,000  
Gross unrealized loss, total in loss position (20,000) (13,000)  
Corporate Bonds [Member]      
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]      
Fair value, in loss position less than twelve months 5,037,000 6,866,000  
Gross unrealized loss, in loss position less than twelve months (35,000) (56,000)  
Fair value, in loss position greater than twelve months 3,395,000 1,847,000  
Gross unrealized loss, in loss position greater than twelve months (12,000) (7,000)  
Fair value, total in loss position 8,432,000 8,713,000  
Gross unrealized loss, total in loss position (47,000) (63,000)  
Other Assets [Member]      
Minority Investments      
Investments in privately-held companies 11,300,000 13,700,000  
Cost method investments $ 0 $ 0 $ 200,000