Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Income tax provision at federal statutory rate			35.00%	35.00%	35.00%
Additional income tax expense due to tax cuts and jobs act of 2017	$ 1,600,000
Provisional amount related to the remeasurement of federal deferred tax assets and liabilities			$ 1,200,000
Provisional amount related to one-time transition tax on mandatory deemed repatriation of foreign earnings			400,000
Cumulative foreign earnings from tax cuts and jobs act of 2017			$ 22,600,000
Tax Cuts and Jobs Act of 2017, accounting complete			false
Income tax benefit from new interpretation of tax law					$ 600,000
Long-term net deferred tax assets	3,500,000		$ 3,500,000	$ 9,800,000
Long-term net deferred tax liabilities	100,000		100,000	100,000
Valuation allowance	2,686,000		2,686,000	2,193,000	1,534,000	$ 1,565,000
Operating loss carryforwards related to a prior acquisition	3,600,000		3,600,000
U.S. federal and state capital loss carryforwards	6,600,000		6,600,000
Deferred tax assets, Capital loss carryforwards expires in 2018	400,000		400,000
Deferred tax assets, Capital loss carryforwards expires in 2020	1,600,000		1,600,000
Deferred tax assets, Capital loss carryforwards expires in 2021	1,400,000		1,400,000
Deferred tax assets, Capital loss carryforwards expires in 2022	3,200,000		3,200,000
Unremitted earnings of U.S. deferred tax liability of foreign subsidiaries	0		0
Unrecognized tax benefits	806,000		806,000	1,774,000	1,910,000	$ 2,136,000
Unrecognized tax benefits that may be settled within next twelve months	400,000		400,000
Accrued interest and penalties related to uncertain tax positions				$ 100,000	$ 200,000
Foreign Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 22,400,000		$ 22,400,000
Scenario, Forecast [Member]
Income Taxes [Line Items]
Income tax provision at federal statutory rate		21.00%