Statutory Financial Information and Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Capital and surplus of the Insurance Companies	$ 66,100,000	$ 58,900,000
Statutory net income (loss) of the Insurance Companies	$ 2,800,000	$ (52,000,000)	$ (7,300,000)
Maximum dividends to be paid as a percentage of statutory capital and surplus without the prior approval of the Texas insurance commissioner	10.00%
Ordinary dividends received	$ 0