Segment Reporting (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011	Mar. 31, 2011		Dec. 31, 2010
Assets
Cash and cash equivalents	$ 151,883		$ 175,012	$ 64,427		$ 66,118
Short term investments	1,316		20,254
Other assets	108,201		106,045
Total consolidated assets	3,226,493		3,264,441
Reportable Segment [Member]
Assets
Total assets for reportable segments	2,965,093		2,963,130
Total consolidated assets	$ 2,965,093	[1]		$ 2,985,895	[1]

[1] Segment assets consist of receivables, prepaids, inventories, property, plant and equipment, and mining properties