Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Uncertain tax positions or unrecognized tax benefits		$ 0	$ 0	$ 0
Accrued interest and penalty	$ 0	$ 0	$ 0
Income taxes at statutory rate, percentage	21.00%	35.00%	35.00%
Income tax expense (benefit)	$ 9,177,000	$ (8,731,000)	$ 17,835,000
Effective tax rate	34.10%	55.90%	38.10%
Derecognition of deferred tax assets	$ 1,825,000
Disallowance of the deductibility dividends paid	$ 1,887,000
Illiquid Assets [Member]
Income Tax Disclosure [Line Items]
Percentage of mandatory one time tax	8.00%
Cash and Cash Equivalents [Member]
Income Tax Disclosure [Line Items]
Percentage of mandatory one time tax	15.50%
Minimum [Member]
Income Tax Disclosure [Line Items]
Percentage of shareholding by controlled foreign corporations and other specified foreign corporations	10.00%