Income Taxes - Additional Information (Detail) - USD ($)		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Reduction in deferred income tax expense related to one-time adjustment to reduce net deferred tax liability		$ 877,400,000	$ 0	$ 0
Reclassification from AOCI to retained earnings	$ 252,000,000
Operating loss carryforwards		22,700,000
Deferred tax assets, valuation allowance		0
Uncertain tax positions		0	0	0
Interest income, net of federal income tax expense		5,000	9,000	$ 11,000
Amount of accrued interest or penalties		$ 0	$ 0