Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2011
Tax Credit Carryforward [Line Items]
Deferred Tax Liabilities, Net	$ 32,000		$ 40,000
Tolling Payment Payable to AFG	147,000
Impact of AMT Repeal on Current Taxes		$ 29,581
Impact of new Tax Law on Deferred Taxes		31,418
Net Impact of New Tax Law		1,886
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	$ 0	$ 0
NOL allocated amount	3,535,000			$ 3,650,000
AFG [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	1,250,000
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$ 3,535,000
Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Minimum [Member] | AFG [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, 2040
Maximum [Member] | AFG [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2034