RETIREMENT FUND AND PROFIT SHARING PLAN, Employees' Savings Plan (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
UNITED STATES | Class A Common Stock [Member]
Compensation Expense [Abstract]
Shares owned by plan (in shares)	121,261
UNITED STATES | Class B Common Stock [Member]
Compensation Expense [Abstract]
Shares owned by plan (in shares)	122,056
401K Plan [Member] | UNITED STATES
Compensation Expense [Abstract]
Compensation expense	$ 0.3	$ 0.3
Retirement Fund [Member] | HONG KONG
Compensation Expense [Abstract]
Compensation expense	$ 0.1	$ 0.1
Retirement Fund [Member] | HONG KONG | Class A Common Stock [Member]
Compensation Expense [Abstract]
Shares owned by plan (in shares)	3,323
Retirement Fund [Member] | HONG KONG | Class B Common Stock [Member]
Compensation Expense [Abstract]
Shares owned by plan (in shares)	17,342