Debt Notes (Details) [Textuals] (USD $)	12 Months Ended						12 Months Ended	0 Months Ended			12 Months Ended				12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Aug. 18, 2011	Aug. 23, 2006	Dec. 31, 2013 3.00% Notes [Member]	Dec. 31, 2013 5.200% Notes [Member]	Aug. 17, 2006 Convertible Debt [Member]	Aug. 18, 2011 Convertible Debt [Member]	Aug. 23, 2006 Convertible Debt [Member]	Dec. 31, 2012 Term Loan [Member]	Dec. 31, 2011 Term Loan [Member]	Dec. 31, 2013 Bridge Loan [Member]	Dec. 31, 2013 DelayedDrawTermLoan [Member]	Dec. 31, 2012 6.625% Notes [Member]	Dec. 31, 2012 5.500% Notes [Member]	Dec. 31, 2012 Bridge Loan [Member]	Dec. 31, 2013 Nontaxable Municipal Bonds [Member]	Dec. 31, 2013 SIFMA [Member] Nontaxable Municipal Bonds [Member] Minimum [Member]	Dec. 31, 2013 SIFMA [Member] Nontaxable Municipal Bonds [Member] Maximum [Member]	Dec. 31, 2013 London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2012 London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2013 Term Loan [Member] London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis																			SIFMA plus 0.860%	SIFMA plus 1.402%	LIBOR plus 1.75%	LIBOR plus 0.50%	LIBOR plus 1.20%
Repayments of Notes Payable	$ 400,000,000	$ 975,991,000	$ 575,641,000				$ 400,000,000								$ 253,900,000	$ 222,100,000
Stated interest rate					3.85%	3.00%	5.20%			3.85%					6.625%	5.50%
Unsecured Notes, face amount											500,000,000
Maturity period of interest rate notes	Sep. 01, 2014							Aug. 15, 2026				Oct. 05, 2012						Nov. 15, 2036
Convertible Debt				482,500,000	650,000,000				482,500,000	650,000,000
Proceeds	1,245,550,000	0	996,190,000
Bridge Loan Principal Amount		2,500,000,000	1,000,000,000
Equity Method Investment, Ownership Percentage	20.00%
Debt Instrument, Fee Amount		10,900,000	2,600,000														8,400,000
Convertible senior subordinated notes conversion ratio								16.3934
Convertible senior subordinated notes, base conversion price										1,000
Debt instrument convertible conversion price per share										$ 61.00
Term Loan Facility Spread	1.20%										0.50%
Write-off of unamortized deferred financing costs	7,400,000	1,600,000									1,000,000		0
Proceeds from Issuance of Unsecured Debt	500,000,000
Proceeds from Debt, Net of Issuance Costs	495,600,000
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Maximum	3.998%
Term Loan Principal Amount														$ 750,000,000