FAIR VALUE MEASUREMENTS - Hierarchy Table (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other precious metal liabilities
Liabilities:
Derivative Liability		$ 8,115
Recurring
Assets:
Financial assets	$ 288,637	316,574
Liabilities:
Financial liabilities	21,632	24,317
Recurring | Marketable securities
Assets:
Financial assets	1,439	58,313
Recurring | Long-term investments
Assets:
Financial assets	257,723	233,360
Recurring | Investments in certain funds
Assets:
Financial assets	422	407
Recurring | Precious metal and commodity inventories recorded at fair value
Assets:
Financial assets	9,884	10,993
Recurring | Economic interests in loans
Assets:
Financial assets	17,156
Recurring | Foreign currency forward exchange contracts
Assets:
Financial assets	275	166
Liabilities:
Financial liabilities	450	188
Recurring | Warrant
Assets:
Financial assets	1,738	206
Recurring | Investment in private company
Assets:
Financial assets	0
Recurring | Long put options
Assets:
Financial assets		3
Recurring | Financial instrument obligations
Liabilities:
Financial liabilities	12,434	15,629
Recurring | Commodity contracts on precious metal and commodity inventories
Assets:
Financial assets		13,126
Liabilities:
Financial liabilities	159	127
Recurring | Short call options
Liabilities:
Financial liabilities		258
Recurring | Level 1
Assets:
Financial assets	210,899	242,117
Liabilities:
Financial liabilities	21,023	24,002
Recurring | Level 1 | Marketable securities
Assets:
Financial assets	836	44,371
Recurring | Level 1 | Long-term investments
Assets:
Financial assets	200,179	186,750
Recurring | Level 1 | Investments in certain funds
Assets:
Financial assets	0	0
Recurring | Level 1 | Precious metal and commodity inventories recorded at fair value
Assets:
Financial assets	9,884	10,993
Recurring | Level 1 | Economic interests in loans
Assets:
Financial assets	0
Recurring | Level 1 | Foreign currency forward exchange contracts
Assets:
Financial assets	0	0
Liabilities:
Financial liabilities	0	0
Recurring | Level 1 | Warrant
Assets:
Financial assets	0	0
Recurring | Level 1 | Investment in private company
Assets:
Financial assets	0
Recurring | Level 1 | Long put options
Assets:
Financial assets		3
Recurring | Level 1 | Financial instrument obligations
Liabilities:
Financial liabilities	12,434	15,629
Recurring | Level 1 | Commodity contracts on precious metal and commodity inventories
Assets:
Financial assets		0
Liabilities:
Financial liabilities	0	0
Recurring | Level 1 | Other precious metal liabilities
Liabilities:
Derivative Liability		8,115
Recurring | Level 1 | Short call options
Liabilities:
Financial liabilities		258
Recurring | Level 2
Assets:
Financial assets	15,821	12,541
Liabilities:
Financial liabilities	609	315
Recurring | Level 2 | Marketable securities
Assets:
Financial assets	603	1,988
Recurring | Level 2 | Long-term investments
Assets:
Financial assets	14,943	10,387
Recurring | Level 2 | Investments in certain funds
Assets:
Financial assets	0	0
Recurring | Level 2 | Precious metal and commodity inventories recorded at fair value
Assets:
Financial assets	0	0
Recurring | Level 2 | Economic interests in loans
Assets:
Financial assets	0
Recurring | Level 2 | Foreign currency forward exchange contracts
Assets:
Financial assets	275	166
Liabilities:
Financial liabilities	450	188
Recurring | Level 2 | Warrant
Assets:
Financial assets	0	0
Recurring | Level 2 | Investment in private company
Assets:
Financial assets	0
Recurring | Level 2 | Long put options
Assets:
Financial assets		0
Recurring | Level 2 | Financial instrument obligations
Liabilities:
Financial liabilities	0	0
Recurring | Level 2 | Commodity contracts on precious metal and commodity inventories
Assets:
Financial assets		0
Liabilities:
Financial liabilities	159	127
Recurring | Level 2 | Other precious metal liabilities
Liabilities:
Derivative Liability		0
Recurring | Level 2 | Short call options
Liabilities:
Financial liabilities		0
Recurring | Level 3
Assets:
Financial assets	61,917	61,916
Liabilities:
Financial liabilities	0	0
Recurring | Level 3 | Marketable securities
Assets:
Financial assets	0	11,954
Recurring | Level 3 | Long-term investments
Assets:
Financial assets	42,601	36,223
Recurring | Level 3 | Investments in certain funds
Assets:
Financial assets	422	407
Recurring | Level 3 | Precious metal and commodity inventories recorded at fair value
Assets:
Financial assets	0	0
Recurring | Level 3 | Economic interests in loans
Assets:
Financial assets	17,156
Recurring | Level 3 | Foreign currency forward exchange contracts
Assets:
Financial assets	0	0
Liabilities:
Financial liabilities	0	0
Recurring | Level 3 | Warrant
Assets:
Financial assets	1,738	206
Recurring | Level 3 | Investment in private company
Assets:
Financial assets	0
Recurring | Level 3 | Long put options
Assets:
Financial assets		0
Recurring | Level 3 | Financial instrument obligations
Liabilities:
Financial liabilities	0	0
Recurring | Level 3 | Commodity contracts on precious metal and commodity inventories
Assets:
Financial assets		13,126
Liabilities:
Financial liabilities	$ 0	0
Recurring | Level 3 | Other precious metal liabilities
Liabilities:
Derivative Liability		0
Recurring | Level 3 | Short call options
Liabilities:
Financial liabilities		$ 0