Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2011
Tax Credit Carryforward [Line Items]
Deferred Tax Liabilities, Net		$ 24,000	$ 32,000
Impact of AMT Repeal on Current Taxes	$ 29,581
Net Impact of New Tax Law	$ 1,886
NOL allocated amount		3,639,000		$ 3,440,000
AFG [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount		1,457,000
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount		$ 3,639,000
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