RETIREMENT FUND AND PROFIT SHARING PLAN, Employees' Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Compensation Expenses [Abstract]
Employer match of the first 1% of compensation contributed by participants	100.00%
Percentage of participant contribution under condition one	1.00%
Employer match of the next 5% compensation contributed by participants, percentage	50.00%
Percentage of employee deferrals under condition two	5.00%
UNITED STATES | Common Class A [Member]
Compensation Expenses [Abstract]
Shares owned by plan (in shares)	114,839
UNITED STATES | Common Class B [Member]
Compensation Expenses [Abstract]
Shares owned by plan (in shares)	127,733
HONG KONG
Compensation Expenses [Abstract]
Employer matching contribution, percentage	7.00%
HONG KONG | Minimum [Member]
Compensation Expenses [Abstract]
Employer matching contribution, percentage	5.00%
HONG KONG | Maximum [Member]
Compensation Expenses [Abstract]
Employee matching contribution per participant under prior plan	5.00%
Retirement Fund [Member] | HONG KONG
Compensation Expenses [Abstract]
Compensation expenses	$ 0.3	$ 0.3
Retirement Fund [Member] | HONG KONG | Common Class A [Member]
Compensation Expenses [Abstract]
Shares owned by plan (in shares)	3,323
Retirement Fund [Member] | HONG KONG | Common Class B [Member]
Compensation Expenses [Abstract]
Shares owned by plan (in shares)	17,342
401K Plan [Member] | UNITED STATES
Compensation Expenses [Abstract]
Compensation expenses	$ 1.3	$ 1.2