Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets:
Total assets	$ 22,619	$ 43,952
Liabilities:
Total liabilities	160,699	184,304
Silver ounces received from Mandalay [Member]
Assets:
Derivative Asset, Fair Value	562	814
Royalty obligation embedded derivative [Member]
Liabilities:
Derivative Liability, Fair Value	146,715	159,400
Put and call options [Member]
Assets:
Derivative Asset, Fair Value		3,040
Liabilities:
Derivative Liability, Fair Value	13,193	20,892
Other derivative instrument [Member]
Liabilities:
Derivative Liability, Fair Value	791	4,012
Short-term Deposit [Member]
Assets:
Short-term Deposits	907	20,254
Marketable securities [Member]
Assets:
Restricted certificates of deposits	21,150	19,844
Fair Value, Inputs, Level 1 [Member]
Assets:
Total assets	22,057	40,098
Liabilities:
Total liabilities	0	0
Fair Value, Inputs, Level 1 [Member] | Silver ounces received from Mandalay [Member]
Assets:
Derivative Asset, Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Royalty obligation embedded derivative [Member]
Liabilities:
Derivative Liability, Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Put and call options [Member]
Assets:
Derivative Asset, Fair Value		0
Liabilities:
Derivative Liability, Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Other derivative instrument [Member]
Liabilities:
Derivative Liability, Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Short-term Deposit [Member]
Assets:
Short-term Deposits	907	20,254
Fair Value, Inputs, Level 1 [Member] | Marketable securities [Member]
Assets:
Restricted certificates of deposits	21,150	19,844
Fair Value, Inputs, Level 2 [Member]
Assets:
Total assets	562	3,854
Liabilities:
Total liabilities	160,699	184,304
Fair Value, Inputs, Level 2 [Member] | Silver ounces received from Mandalay [Member]
Assets:
Derivative Asset, Fair Value	562	814
Fair Value, Inputs, Level 2 [Member] | Royalty obligation embedded derivative [Member]
Liabilities:
Derivative Liability, Fair Value	146,715	159,400
Fair Value, Inputs, Level 2 [Member] | Put and call options [Member]
Assets:
Derivative Asset, Fair Value		3,040
Liabilities:
Derivative Liability, Fair Value	13,193	20,892
Fair Value, Inputs, Level 2 [Member] | Other derivative instrument [Member]
Liabilities:
Derivative Liability, Fair Value	791	4,012
Fair Value, Inputs, Level 2 [Member] | Short-term Deposit [Member]
Assets:
Short-term Deposits	0	0
Fair Value, Inputs, Level 2 [Member] | Marketable securities [Member]
Assets:
Restricted certificates of deposits	0	0
Fair Value, Inputs, Level 3 [Member]
Assets:
Total assets	0	0
Liabilities:
Total liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Silver ounces received from Mandalay [Member]
Assets:
Derivative Asset, Fair Value	0	0
Fair Value, Inputs, Level 3 [Member] | Royalty obligation embedded derivative [Member]
Liabilities:
Derivative Liability, Fair Value	0	0
Fair Value, Inputs, Level 3 [Member] | Put and call options [Member]
Assets:
Derivative Asset, Fair Value		0
Liabilities:
Derivative Liability, Fair Value	0	0
Fair Value, Inputs, Level 3 [Member] | Other derivative instrument [Member]
Liabilities:
Derivative Liability, Fair Value	0	0
Fair Value, Inputs, Level 3 [Member] | Short-term Deposit [Member]
Assets:
Short-term Deposits	0	0
Fair Value, Inputs, Level 3 [Member] | Marketable securities [Member]
Assets:
Restricted certificates of deposits	$ 0	$ 0
Convertible Senior Notes Due March 2028 [Member]
Liabilities:
Debt Instrument, Interest Rate, Stated Percentage	3.25%