Investments (Amortized Cost, Gross Unrealized Gains And Losses And Estimated Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current Investments [Member]
Schedule of Investments [Line Items]
Amortized Cost	$ 121,421	$ 146,594
Gross Unrealized Gains	25	83
Gross Unrealized Losses	6	700
Estimated Fair Value	121,440	145,977
Current Investments [Member] | U.S. Government And Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	116,928	139,940
Gross Unrealized Gains	7	13
Gross Unrealized Losses	6	1
Estimated Fair Value	116,929	139,952
Current Investments [Member] | All Other Corporates [Member]
Schedule of Investments [Line Items]
Amortized Cost	4,160	5,649
Gross Unrealized Gains	18	70
Estimated Fair Value	4,178	5,719
Current Investments [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	121,088	145,589
Gross Unrealized Gains	25	83
Gross Unrealized Losses	6	1
Estimated Fair Value	121,107	145,671
Current Investments [Member] | Other Investments [Member]
Schedule of Investments [Line Items]
Amortized Cost	333	1,005
Gross Unrealized Losses		699
Estimated Fair Value	333	306
Non-Current Investments [Member]
Schedule of Investments [Line Items]
Amortized Cost	1,256,251	1,344,373
Gross Unrealized Gains	331,457	711,476
Gross Unrealized Losses	1,189	1,956
Estimated Fair Value	1,586,519	2,053,893
Non-Current Investments [Member] | U.S. Government And Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	10,004
Gross Unrealized Losses	18
Estimated Fair Value	9,986
Non-Current Investments [Member] | Equity Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	579,603	666,801
Gross Unrealized Gains	315,908	698,157
Gross Unrealized Losses	82	299
Estimated Fair Value	895,429	1,364,659
Non-Current Investments [Member] | Common Stocks: Banks, Trusts And Insurance Companies [Member]
Schedule of Investments [Line Items]
Amortized Cost	22,084	22,084
Gross Unrealized Gains	25,939	28,887
Estimated Fair Value	48,023	50,971
Non-Current Investments [Member] | Common Stocks: Industrial, Miscellaneous And All Other [Member]
Schedule of Investments [Line Items]
Amortized Cost	557,519	644,717
Gross Unrealized Gains	289,969	669,270
Gross Unrealized Losses	82	299
Estimated Fair Value	847,406	1,313,688
Non-Current Investments [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	676,648	676,577
Gross Unrealized Gains	15,549	13,319
Gross Unrealized Losses	1,107	1,163
Estimated Fair Value	691,090	688,733
Non-Current Investments [Member] | U.S. Government-Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Amortized Cost	585,312	609,617
Gross Unrealized Gains	14,912	12,683
Gross Unrealized Losses	48	109
Estimated Fair Value	600,176	622,191
Non-Current Investments [Member] | Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	81,332	66,960
Gross Unrealized Gains	637	636
Gross Unrealized Losses	1,041	1,054
Estimated Fair Value	80,928	66,542
Non-Current Investments [Member] | Other Investments [Member]
Schedule of Investments [Line Items]
Amortized Cost		995
Gross Unrealized Losses		494
Estimated Fair Value		$ 501