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Income Taxes - Schedule of Reconciliation of Federal Statutory Rate on Loss before Income Taxes and before Gain from Sale of Equity Method Investment Rate to Effective Income Tax Rate (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Tax Disclosure [Abstract]      
Statutory federal tax rate (21.00%) (34.00%) (34.00%)
State income taxes, net of federal income tax benefit 3.60% 97.20% 1.90%
Increase (decrease) in valuation allowance (9.10%) (936.10%) 46.50%
Permanent items (5.90%) (861.20%) 0.90%
Tax credits (5.50%) (1222.30%) (13.60%)
Provision vs. tax return differences (1.70%)    
Foreign rate differential and deferred items 0.70% (91.80%) (0.80%)
Decrease in tax reserves 0.10% (5.10%)  
Rate change due to tax reform   3441.10%  
Refundable income taxes - AMT credit   (751.00%)  
Capital gain on sale to noncontrolling interest     3.90%
Decrease in unremitted Vicor Custom Power earnings     (0.90%)
Book income attributable to noncontrolling interest     0.10%
Other 0.10% (0.10%) (0.20%)
Effective income tax rate 3.30% (363.30%) 3.80%