Long-Term Debt (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) TradingDays / d shares $ / shares	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,850,000
Line of Credit Facility, Borrowing Capacity, Term	5 years
Increase in revolver capacity	$ 350,000
Line of Credit Facility, Initiation Date	Jul. 27, 2012
Line of Credit Facility, Expiration Date	Jul. 27, 2017
Line of Credit Facility, Amount Outstanding	$ 180,000
Outstanding letters of credit	$ 43,300
Debt covenant compliance	3.5
Debt Instrument [Line Items]
Total Debt	$ 3,271,222	$ 2,201,374
Unamortized Debt Issuance Expense	(17,392)	(12,749)
Current Portion	6,805	11,092
Long-term debt, net of current portion	3,264,417	2,190,282
Principal amount	3,100
Future maturities of long term debt [Abstract]
2016	6,805
2017	581,296
2018	800,460
2019	500,053
2020	600,000
Thereafter	800,000
Total	3,288,614
Credit Facility Member 2012 [Member]
Debt Instrument [Line Items]
Principal amount	$ 180,000	0
Senior Notes 2017 [Member]
Debt Instrument [Line Items]
Issuance Date	Nov. 21, 2012
Interest rate (in hundredths)	1.85%
Principal amount	$ 400,000	400,000
Periodic interest payments	semi-annually
Periodic interest payments, start	May 15, 2013
Maturity Date	Nov. 15, 2017
Senior Notes 2018 [Member]
Debt Instrument [Line Items]
Issuance Date	Jun. 06, 2013
Interest rate (in hundredths)	2.05%
Principal amount	$ 800,000	800,000
Periodic interest payments	semi-annually
Periodic interest payments, start	October 1, 2013
Maturity Date	Oct. 01, 2018
Senior Notes 2019 [Member]
Debt Instrument [Line Items]
Issuance Date	Sep. 15, 2009
Interest rate (in hundredths)	6.25%
Principal amount	$ 500,000	500,000
Periodic interest payments	semi-annually
Periodic interest payments, start	March 1, 2010
Maturity Date	Sep. 01, 2019
Senior Notes 2020 [Member]
Debt Instrument [Line Items]
Issuance Date	Dec. 07, 2015
Interest rate (in hundredths)	3.00%
Principal amount	$ 600,000	0
Periodic interest payments	semi-annually
Periodic interest payments, start	June 15, 2016
Maturity Date	Dec. 15, 2020
Senior Notes 2022 [Member]
Debt Instrument [Line Items]
Issuance Date	Nov. 21, 2012
Interest rate (in hundredths)	3.125%
Principal amount	$ 500,000	500,000
Periodic interest payments	semi-annually
Periodic interest payments, start	May 15, 2013
Maturity Date	Nov. 15, 2022
Senior Notes 2025 [Member]
Debt Instrument [Line Items]
Issuance Date	Dec. 07, 2015
Interest rate (in hundredths)	3.85%
Principal amount	$ 300,000	0
Periodic interest payments	semi-annually
Periodic interest payments, start	June 15, 2016
Maturity Date	Dec. 15, 2025
Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount	$ 4,179	8,003
Capital Lease Obligations And Foreign Letter Of Credit Issuance [Member]
Debt Instrument [Line Items]
Principal amount	$ 4,435	$ 6,120
Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Interest rate (in hundredths)	3.75%
Maturity Date	Dec. 31, 2034
Subordinated Convertible Notes
Subordinated convertible notes, original public offering amount	$ 230,000
Original issue discount (in hundredths)	60.498%
Subordinated convertible note holding period for contingent cash interest	180
Trading days the average price of subordinated convertible note must meet threshold within six months measurement period	5
Commencement date for measurement of average trading price on a subordinated convertible note	Jan. 15, 2009
Contingent cash interest payable annual rate if threshold is met (in hundredths)	0.25%
Debt Instrument Convertible Price Next Conversion Date | $ / shares	$ 572.76
Next conversion date	1/15/2019
Convertible notes purchase price on January 15, 2019 (third conversion date) | $ / shares	$ 689.68
Third conversion date	1/15/2024
Convertible notes purchase price on January 15, 2024 (fourth conversion date) | $ / shares	$ 830.47
Fourth conversion date	1/15/2029
Minimum number of trading days in the consecutive trading period that the common stock sale price above threshold to trigger conversion (in days) | TradingDays / d	20
Number of consecutive trading days in the preceding quarter the minimum trading days must occur in for the sale price to reach threshold to trigger conversion (in days) | TradingDays / d	30
Conversion price, end of period | $ / shares	$ 511.62
If converted, the value exceeding principal amount outstanding at end of period	$ 16,000
If converted, issuance of common stock shares | shares	81,778