Financial Instruments (Fair Value Of Investments) (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Marketable investment securities available for sale in an unrealized loss position
In Loss Position for Less Than 12 Months, Fair Value	$ 38,236	$ 45,084
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	32	35
In Loss Position for More Than 12 Months, Fair Value	0	0
In Loss Position for More Than 12 Months, Gross Unrealized Losses	0	0
Total, Fair Value	38,236	45,084
Total, Gross Unrealized Losses	32	35
Corporate
Marketable investment securities available for sale in an unrealized loss position
In Loss Position for Less Than 12 Months, Fair Value	33,304	37,974
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	31	31
In Loss Position for More Than 12 Months, Fair Value	0	0
In Loss Position for More Than 12 Months, Gross Unrealized Losses	0	0
Total, Fair Value	33,304	37,974
Total, Gross Unrealized Losses	31	31
Government agency
Marketable investment securities available for sale in an unrealized loss position
In Loss Position for Less Than 12 Months, Fair Value	4,932	7,110
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	1	4
In Loss Position for More Than 12 Months, Fair Value	0	0
In Loss Position for More Than 12 Months, Gross Unrealized Losses	0	0
Total, Fair Value	4,932	7,110
Total, Gross Unrealized Losses	$ 1	$ 4