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Investments and Fair Value Measurements - Investment Category and Length (Details) - USD ($)
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]      
Fair value, in loss position less than twelve months $ 11,375,000 $ 8,262,000  
Gross unrealized loss, in loss position less than twelve months (67,000) (40,000)  
Fair value, in loss position greater than twelve months 5,390,000 4,309,000  
Gross unrealized loss, in loss position greater than twelve months (9,000) (2,000)  
Fair value, total in loss position 16,765,000 12,571,000  
Gross unrealized loss, total in loss position (76,000) (42,000)  
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 4,509,000 4,492,000  
Gross unrealized loss, in loss position less than twelve months (11,000) (13,000)  
Fair value, in loss position greater than twelve months 3,543,000    
Gross unrealized loss, in loss position greater than twelve months (2,000)    
Fair value, total in loss position 8,052,000 4,492,000  
Gross unrealized loss, total in loss position (13,000) (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 6,866,000 3,770,000  
Gross unrealized loss, in loss position less than twelve months (56,000) (27,000)  
Fair value, in loss position greater than twelve months 1,847,000 4,309,000  
Gross unrealized loss, in loss position greater than twelve months (7,000) (2,000)  
Fair value, total in loss position 8,713,000 8,079,000  
Gross unrealized loss, total in loss position (63,000) (29,000)  
Other Assets [Member]      
Minority Investments [Abstract]      
Investments in privately-held companies 12,100,000 12,100,000  
Minority investments in unconsolidated privately-held companies $ 0 $ 200,000 $ 200,000