Fair Value Measurements Hierarchy Table (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets:
Total	$ 406,361	$ 453,720
Liabilities:
Total	21,282	21,449
Marketable securities
Assets:
Marketable securities	120,499	138,457
Long-term investments
Assets:
Long-term investments	269,022	300,725
Investments in certain funds
Assets:
Investments in certain funds	468	525
Precious metal and commodity inventories recorded at fair value
Assets:
Precious metal and commodity inventories recorded at fair value	13,195	13,249
Commodity contracts on precious metal and commodity inventories
Assets:
Commodity contracts on precious metal and commodity inventories	846	764
Foreign currency forward exchange contracts
Assets:
Commodity contracts on precious metal and commodity inventories	2,331
Financial instruments
Liabilities:
Financial instruments	21,385	21,311
Interest rate swap agreement
Liabilities:
Financial instruments	(103)	138
Level 1
Assets:
Total	353,118	394,521
Liabilities:
Total	21,385	21,311
Level 1 | Marketable securities
Assets:
Marketable securities	74,808	93,768
Level 1 | Long-term investments
Assets:
Long-term investments	265,115	286,740
Level 1 | Investments in certain funds
Assets:
Investments in certain funds	0	0
Level 1 | Precious metal and commodity inventories recorded at fair value
Assets:
Precious metal and commodity inventories recorded at fair value	13,195	13,249
Level 1 | Commodity contracts on precious metal and commodity inventories
Assets:
Commodity contracts on precious metal and commodity inventories	0	764
Level 1 | Foreign currency forward exchange contracts
Assets:
Commodity contracts on precious metal and commodity inventories	0
Level 1 | Financial instruments
Liabilities:
Financial instruments	21,385	21,311
Level 1 | Interest rate swap agreement
Liabilities:
Financial instruments	0	0
Level 2
Assets:
Total	13,852	10,793
Liabilities:
Total	(103)	138
Level 2 | Marketable securities
Assets:
Marketable securities	10,675	10,793
Level 2 | Long-term investments
Assets:
Long-term investments	0	0
Level 2 | Investments in certain funds
Assets:
Investments in certain funds	0	0
Level 2 | Precious metal and commodity inventories recorded at fair value
Assets:
Precious metal and commodity inventories recorded at fair value	0	0
Level 2 | Commodity contracts on precious metal and commodity inventories
Assets:
Commodity contracts on precious metal and commodity inventories	846	0
Level 2 | Foreign currency forward exchange contracts
Assets:
Commodity contracts on precious metal and commodity inventories	2,331
Level 2 | Financial instruments
Liabilities:
Financial instruments	0	0
Level 2 | Interest rate swap agreement
Liabilities:
Financial instruments	(103)	138
Level 3
Assets:
Total	39,391	48,406
Liabilities:
Total	0	0
Level 3 | Marketable securities
Assets:
Marketable securities	35,016	33,896
Level 3 | Long-term investments
Assets:
Long-term investments	3,907	13,985
Level 3 | Investments in certain funds
Assets:
Investments in certain funds	468	525
Level 3 | Precious metal and commodity inventories recorded at fair value
Assets:
Precious metal and commodity inventories recorded at fair value	0	0
Level 3 | Commodity contracts on precious metal and commodity inventories
Assets:
Commodity contracts on precious metal and commodity inventories	0	0
Level 3 | Foreign currency forward exchange contracts
Assets:
Commodity contracts on precious metal and commodity inventories	0
Level 3 | Financial instruments
Liabilities:
Financial instruments	0	0
Level 3 | Interest rate swap agreement
Liabilities:
Financial instruments	$ 0	$ 0