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Income Taxes - Additional Information (Detail)
£ in Millions
6 Months Ended 12 Months Ended
Dec. 31, 2018
USD ($)
Dec. 31, 2017
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Dec. 31, 2018
GBP (£)
Unrecognized tax benefits $ 0   $ 0 $ 0    
Accrued penalties or interest related to uncertain tax positions $ 0   $ 0 $ 0    
Statutory federal corporate income tax rate 21.00% 34.00% 27.50% 34.00% 34.00%  
Foreign current income tax benefit         $ 159,000  
Changes in valuation allowance $ 7,166,000   $ (5,385,000) $ 7,489,000 $ 6,789,000  
U.S. Federal [Member]            
Operating loss carry forwards $ 185,900,000          
Tax years that remain subject to examination 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017          
Operating loss carry forwards, expiration range start dates 2023          
Operating loss carry forwards, expiration range end dates 2038          
State [Member]            
Operating loss carry forwards $ 144,300,000          
Federal And State Tax [Member]            
Research and development tax credit carry forwards expiration begin date 2018          
Research and development tax credit carry forwards expiration end date 2038          
United Kingdom Tax Authority [Member]            
Operating loss carry forwards $ 26,700,000         £ 21.0
Tax years that remain subject to examination 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017          
Federal and State Research and Development Tax Credit Carryforward [Member]            
Research and development tax credit carry forwards $ 3,100,000          
Icon Bioscience Inc [Member]            
Deferred tax asset 6,200,000          
Icon Bioscience Inc [Member] | U.S. Federal [Member]            
Operating loss carry forwards $ 49,300,000