Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended
	Jun. 30, 2017	Sep. 30, 2011	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Tolling Payment Payable to AFG, Gross	$ 2,605		$ 28,691
Income Tax Examination, Penalties and Interest Accrued		$ 3,650,000
NOL allocated amount	4,019,178
AFG [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	1,386,696
Percentage Of Notional Federal Tax Liability		50.00%
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	3,931,962
Capital Loss Carryforward [Member] | United States [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$ 87,216
Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Maximum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2033