Fair Value Measurements (Assets Measured At Fair Value On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in money market and short term treasury instruments	$ 148,985	$ 177,816
Retained interest in entities	10,707	10,283	9,881
Total	159,692	188,099
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in money market and short term treasury instruments	148,985	177,816
Total	148,985	177,816
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in money market and short term treasury instruments
Retained interest in entities
Total
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Retained interest in entities	10,707	10,283
Total	$ 10,707	$ 10,283