Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Sep. 30, 2011
Tax Credit Carryforward [Line Items]
NOL allocated amount		$ 3,650,000
Afg [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$ 1,398,666
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
NOL allocated amount	$ 3,451,870
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, 2032