Marketable Securities (Company's Marketable Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Company's Marketable Securities
Marketable Securities, Amortized Cost	$ 268,245	$ 287,390
Marketable Securities, Gross Unrealized Gains	1,583	1,314
Marketable Securities, Gross Unrealized Losses	(677)	(1,623)
Estimated Fair Value, Total	269,151	287,081
Debt Securities [Member]
Company's Marketable Securities
Amortized Cost	251,494	270,745
Gross Unrealized Gains	487	1,298
Gross Unrealized Losses	(677)	(191)
Estimated Fair Value, Securities	251,304	271,852
Equity Securities [Member]
Company's Marketable Securities
Amortized Cost	10,518	10,518
Gross Unrealized Gains	688	0
Gross Unrealized Losses	0	(1,344)
Estimated Fair Value, Securities	11,206	9,174
Estimated Fair Value, Total	11,206	9,174
Mutual Funds [Member]
Company's Marketable Securities
Mutual Funds, Amortized Cost	6,233	6,127
Mutual Funds, Gross Unrealized Gains	408	16
Mutual Funds, Gross Unrealized Losses	0	(88)
Estimated Fair Value, Mutual funds	6,641	6,055
Estimated Fair Value, Total	$ 6,641	$ 6,055