Financial Instruments (Fair Value Of Investments) (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Marketable investment securities available for sale in an unrealized loss position
In Loss Position for Less Than 12 Months, Fair Value	$ 80,391	$ 74,407
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	61	56
In Loss Position for More Than 12 Months, Fair Value	0	5,732
In Loss Position for More Than 12 Months, Gross Unrealized Losses	0	4
Total, Fair Value	80,391	80,139
Total, Gross Unrealized Losses	61	60
Corporate
Marketable investment securities available for sale in an unrealized loss position
In Loss Position for Less Than 12 Months, Fair Value	79,932	74,407
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	61	56
In Loss Position for More Than 12 Months, Fair Value	0	5,732
In Loss Position for More Than 12 Months, Gross Unrealized Losses	0	4
Total, Fair Value	79,932	80,139
Total, Gross Unrealized Losses	61	60
Government agency
Marketable investment securities available for sale in an unrealized loss position
In Loss Position for Less Than 12 Months, Fair Value	459	0
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	0	0
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	459	0
Total, Gross Unrealized Losses	$ 0	$ 0