Investments (Fair Value of Investments Available-for-Sale) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Carrying Value, Current	$ 1,580,032,000	$ 1,812,512,000
Carrying Value, Noncurrent	52,637,000	0
Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,611,091,000	1,753,931,000
Gross Unrealized Holding Gains	13,600,000	61,300,000
Gross Unrealized Holding Losses	(44,700,000)	(2,700,000)
Carrying Value, Current	1,580,000,000	1,812,500,000
Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	60,080,000	0
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	(7,500,000)
Carrying Value, Noncurrent	52,600,000
Asset-Backed Securities [Member] \| Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	410,100,000	499,700,000
Gross Unrealized Holding Gains	3,900,000	19,600,000
Gross Unrealized Holding Losses	(6,600,000)	(200,000)
Carrying Value, Current	407,400,000	519,100,000
Asset-Backed Securities [Member] \| Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	800,000
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	(100,000)
Carrying Value, Noncurrent	700,000
U.S. Government and Agencies [Member] \| Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,500,000	25,900,000
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Carrying Value, Current	26,500,000	25,900,000
Obligations of States and Other Political Subdivisions [Member] \| Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	741,100,000	819,900,000
Gross Unrealized Holding Gains	6,400,000	24,200,000
Gross Unrealized Holding Losses	(28,300,000)	(2,000,000)
Carrying Value, Current	719,200,000	842,100,000
Obligations of States and Other Political Subdivisions [Member] \| Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,900,000
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	(6,000,000)
Carrying Value, Noncurrent	42,900,000
Corporate Debt Securities [Member] \| Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	433,400,000	408,400,000
Gross Unrealized Holding Gains	3,300,000	17,500,000
Gross Unrealized Holding Losses	(9,800,000)	(500,000)
Carrying Value, Current	426,900,000	425,400,000
Corporate Debt Securities [Member] \| Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,400,000
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	(1,400,000)
Carrying Value, Noncurrent	$ 9,000,000

- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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