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Income Taxes - Reconciliation of Provision for Income Taxes from Continuing Operations (Parenthetical) (Detail)
4 Months Ended 8 Months Ended 12 Months Ended
Apr. 30, 2018
Dec. 31, 2017
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2016
Income Tax Disclosure [Abstract]          
Federal income taxes, expected statutory rate 21.00% 35.00% 30.40% 35.00% 35.00%