Reconciliation of Provision for Income Taxes Based on Income (Loss) Before Federal Income Taxes, Computed using Federal Statutory Rate Versus Reported Provision for Income Taxes (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	35.00%	35.00%