Fair Value Measurements And Marketable Securities (Schedule Of Marketable Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 90,379		$ 69,411
Gross Unrealized Gain (Loss)	17,599	[1]	13,059	[1]
Estimated Fair Value	107,978		82,470
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	21,430
Estimated Fair Value	39,016
Securities In Unrealized Gain Position [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	47,808		38,606
Gross Unrealized Gain (Loss)	17,611	[1]	13,067	[1]
Estimated Fair Value	65,419		51,673
Securities In Unrealized Gain Position [Member] | Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	21,430		22,376
Gross Unrealized Gain (Loss)	17,586	[1]	13,049	[1]
Estimated Fair Value	39,016		35,425
Securities In Unrealized Gain Position [Member] | Corporate Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5,182		4,211
Gross Unrealized Gain (Loss)	7	[1]	4	[1]
Estimated Fair Value	5,189		4,215
Securities In Unrealized Gain Position [Member] | Government Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	19,191	[2]	4,495	[2]
Gross Unrealized Gain (Loss)	18	[1],[2]	14	[1],[2]
Estimated Fair Value	19,209	[2]	4,509	[2]
Securities In Unrealized Gain Position [Member] | Government Sponsored Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost			3,501	[3]
Gross Unrealized Gain (Loss)		[1],[3]		[1],[3]
Estimated Fair Value			3,501	[3]
Securities In Unrealized Gain Position [Member] | U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	2,005		4,023
Gross Unrealized Gain (Loss)		[1]		[1]
Estimated Fair Value	2,005		4,023
Securities In Unrealized Loss Position [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	16,521		13,095
Gross Unrealized Gain (Loss)	(12)	[1]	(8)	[1]
Estimated Fair Value	16,509		13,087
Securities In Unrealized Loss Position [Member] | Corporate Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5,332		4,844
Gross Unrealized Gain (Loss)	(7)	[1]	(7)	[1]
Estimated Fair Value	5,325		4,837
Securities In Unrealized Loss Position [Member] | Government Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,942
Gross Unrealized Gain (Loss)		[1]		[1]
Estimated Fair Value	1,942
Securities In Unrealized Loss Position [Member] | Government Sponsored Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,242
Gross Unrealized Gain (Loss)	(5)	[1]		[1]
Estimated Fair Value	7,237
Securities In Unrealized Loss Position [Member] | U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	2,005		8,251
Gross Unrealized Gain (Loss)		[1]	(1)	[1]
Estimated Fair Value	2,005		8,250
Securities At Amortized Cost [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	26,050		17,710
Gross Unrealized Gain (Loss)		[1]		[1]
Estimated Fair Value	26,050		17,710
Securities At Amortized Cost [Member] | Time Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	26,050		16,920
Gross Unrealized Gain (Loss)		[1]		[1]
Estimated Fair Value	26,050		16,920
Securities At Amortized Cost [Member] | Corporate Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost			790
Gross Unrealized Gain (Loss)		[1]		[1]
Estimated Fair Value			$ 790

[1] Unrealized gains or losses of less than $1,000 for each category are reflected as a dash.

[2] State and municipal government debt obligations.

[3] Government sponsored enterprise.