Investments (Available for Sale Current and Noncurrent Investments Classified by Contractual Maturity Date) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Current	$ 1,567,020,000	$ 1,812,512,000
Noncurrent	59,768,000	0
Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	47,800,000
Due after one year through five years, Amortized Cost	312,200,000
Due after five years through ten years, Amortized Cost	432,700,000
Due after ten years, Amortized Cost	415,100,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	394,700,000
Available-for-sale Securities, Amortized Cost Basis	1,602,456,000	1,753,931,000
Due in one year or less, Estimated Fair Value	48,000,000
Due after one year through five years, Estimated Fair Value	314,700,000
Due after five years through ten years, Estimated Fair Value	424,700,000
Due after ten years, Estimated Fair Value	390,200,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	389,400,000
Current	1,567,000,000	1,812,500,000
Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Due after one year through five years, Amortized Cost	1,000,000
Due after five years through ten years, Amortized Cost	7,900,000
Due after ten years, Amortized Cost	57,700,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	1,300,000
Available-for-sale Securities, Amortized Cost Basis	67,943,000	0
Due after one year through five years, Estimated Fair Value	800,000
Due after five years through ten years, Estimated Fair Value	7,000,000
Due after ten years, Estimated Fair Value	50,900,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	1,100,000
Noncurrent	$ 59,800,000