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Investments and Fair Value Measurements - Investment Category and Length (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
entity
Mar. 31, 2017
USD ($)
company
Mar. 31, 2017
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2016
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 $ 25,884,000 $ 25,884,000 $ 25,884,000   $ 10,248,000
Gross unrealized loss, in loss position less than twelve months     (78,000)   (55,000)
Fair value, in loss position greater than twelve months 1,942,000 1,942,000 1,942,000   4,595,000
Gross unrealized loss, in loss position greater than twelve months     (1,000)   (12,000)
Fair value, total in loss position 27,826,000 27,826,000 27,826,000   14,843,000
Gross unrealized loss, total in loss position     (79,000)   (67,000)
Minority Investments          
Investments in privately-held companies $ 6,274,000 $ 6,274,000 6,274,000   6,599,000
Equity method investments 3 7      
Investments held $ 6,274,000 $ 6,274,000 6,274,000   6,599,000
One Gallium Company          
Minority Investments          
Investments in privately-held companies 0 0 0    
Impairment charge     313,000 $ 0  
Investments held 0 0 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 4,260,000 4,260,000 4,260,000   5,211,000
Gross unrealized loss, in loss position less than twelve months     (10,000)   (20,000)
Fair value, in loss position greater than twelve months 240,000 240,000 240,000   1,200,000
Fair value, total in loss position 4,500,000 4,500,000 4,500,000   6,411,000
Gross unrealized loss, total in loss position     (10,000)   (20,000)
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 21,624,000 21,624,000 21,624,000   5,037,000
Gross unrealized loss, in loss position less than twelve months     (68,000)   (35,000)
Fair value, in loss position greater than twelve months 1,702,000 1,702,000 1,702,000   3,395,000
Gross unrealized loss, in loss position greater than twelve months     (1,000)   (12,000)
Fair value, total in loss position 23,326,000 23,326,000 23,326,000   8,432,000
Gross unrealized loss, total in loss position     (69,000)   (47,000)
Other Assets [Member]          
Minority Investments          
Investments in privately-held companies 10,400,000 10,400,000 10,400,000   11,300,000
Investments held $ 10,400,000 $ 10,400,000 $ 10,400,000   $ 11,300,000