Exchangeable Senior Notes (Additional Information About Senior Notes) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Debt Instrument [Line Items]
Coupon interest	$ 130,583	$ 124,126	$ 121,765
Discount amortization	1,782	2,082	1,967
Senior Notes [Member]
Debt Instrument [Line Items]
Coupon interest	4,835	5,775	5,775
Issuance cost amortization	456	547	547
Discount amortization	1,782	2,082	1,968
Total interest expense	$ 7,073	$ 8,404	$ 8,290