Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Reconciliation [Line Items]
Estimated effective income tax rate	50.00%	30.00%	55.00%
Valuation allowance for deferred tax assets	$ 3,088,000	$ 5,731,000
Deferred tax assets related to net operating losses for federal income tax purposes	$ 16,769,000	20,272,000
Ownership percentage	50.00%
Percentage increasing ownership	5.00%
Pre-tax net operating loss carryovers	$ 12,600,000
Built-in losses annual limitation	1,100,000
Interest or penalties related to unrecognized tax benefits	0	0	$ 0
Effect of U.S. tax reform (the Tax Act)	13,074,000	$ 0	$ 0
Federal
Income Tax Reconciliation [Line Items]
Deferred tax assets related to net operating losses for federal income tax purposes	8,500,000
State
Income Tax Reconciliation [Line Items]
Deferred tax assets related to net operating losses for federal income tax purposes	$ 8,300,000