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RETIREMENT FUND AND PROFIT SHARING PLAN, Employees' Savings Plan (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Class A Common Stock [Member] | UNITED STATES |  |  |  |
Compensation Expense [Abstract] |  |  |  |
Shares owned by plan (in shares) | 90,521 |  | 90,521 |
Class B Common Stock [Member] | UNITED STATES |  |  |  |
Compensation Expense [Abstract] |  |  |  |
Shares owned by plan (in shares) | 140,591 |  | 140,591 |
401K Plan [Member] | UNITED STATES |  |  |  |
Compensation Expense [Abstract] |  |  |  |
Compensation expense | $ 0.3 | $ 0.3 | $ 0.6 | $ 0.6
Retirement Fund [Member] | HONG KONG |  |  |  |
Compensation Expense [Abstract] |  |  |  |
Compensation expense | $ 0.1 | $ 0.1 | $ 0.2 | $ 0.2
Retirement Fund [Member] | Class A Common Stock [Member] | HONG KONG |  |  |  |
Compensation Expense [Abstract] |  |  |  |
Shares owned by plan (in shares) | 3,323 |  | 3,323 |
Retirement Fund [Member] | Class B Common Stock [Member] | HONG KONG |  |  |  |
Compensation Expense [Abstract] |  |  |  |
Shares owned by plan (in shares) | 17,342 |  | 17,342 |

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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