Financial Instruments (Cash And Cash Equivalents And Investments From Continuing Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Cash, Cost	$ 109,592	$ 157,317
Money market funds, Cost	119,335	122,827
Total cash and cash equivalents, Cost	228,927	280,144
Total short-term investments (available-for-sale), Cost	160,498	160,610
Total cash and cash equivalents and short-term investments, Cost	389,425	440,754
Cash, Gross Unrealized Gain
Money market funds, Gross Unrealized Gain	461	448
Total cash and cash equivalents, Gross Unrealized Gain	461	448
Total short-term investments (available-for-sale), Gross Unrealized Gain	6	31
Total cash and cash equivalents and short-term investments, Gross Unrealized Gain	467	479
Cash, Gross Unrealized (Loss)
Money market funds, Gross Unrealized (Loss)
Total cash and cash equivalents, Gross Unrealized (Loss)
Total short-term investments (available-for-sale), Gross Unrealized (Loss)	(35)	(34)
Total cash and cash equivalents and short-term investments, Gross Unrealized (Loss)	(35)	(34)
Cash, Fair Value	109,592	157,317
Money market funds, Fair Value	119,796	123,275
Total cash and cash equivalents, Fair Value	229,388	280,592	214,125	260,644
Long-term investments (available-for-sale), Fair Value	170,884	171,022
Total short-term investments (available-for-sale), Fair Value	160,469	160,607
Total cash and cash equivalents and short-term investments, Fair Value	389,857	441,199
Municipal Bonds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Long-term investments (available-for-sale), Cost	11,150	11,150
Long-term investments (available-for-sale), Gross Unrealized Gain
Long-term investments (available-for-sale), Gross Unrealized (Loss)	(735)	(735)
Long-term investments (available-for-sale), Fair Value	10,415	10,415
Total investments at fair value	10,415	10,415
U.S. Treasury Bills [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Short-term investments (available-for-sale), Cost	120,507	133,648
Short-term investments (available-for-sale), Gross Unrealized Gain	6	31
Short-term investments (available-for-sale), Gross Unrealized (Loss)	(26)	(5)
Long-term investments (available-for-sale), Fair Value	120,487	133,674
U.S. Government Agencies [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Short-term investments (available-for-sale), Cost	39,991	26,962
Short-term investments (available-for-sale), Gross Unrealized Gain
Short-term investments (available-for-sale), Gross Unrealized (Loss)	(9)	(29)
Long-term investments (available-for-sale), Fair Value	$ 39,982	$ 26,933