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Long-Term Debt - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]      
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net $ 42,300 $ 42,300 $ 44,300
Line of credit facility, maturity date   Apr. 09, 2023  
Aggregate amount of lender commitments on credit facility 1,500,000 $ 1,500,000  
Line of Credit Facility, Maximum Borrowing Capacity $ 4,000,000 4,000,000  
Line of credit facility, commitment fee percentage, per annum 0.20%    
Current portion of long-term debt $ 2,322 $ 2,322 2,286
Line of Credit Facility, Covenant Terms   0.65  
4.5% Senior Notes due 2023      
Debt Instrument [Line Items]      
Debt Instrument, stated interest rate 4.50% 4.50%  
Debt Instrument, Maturity Date, Description   2023  
Note payable      
Debt Instrument [Line Items]      
Notes Payable $ 22,000 $ 22,000  
Loan term   10 years  
Debt Instrument, stated interest rate 3.14% 3.14%  
Debt Instrument, Maturity Date   Feb. 26, 2022  
5% Senior Notes due 2022 (1)      
Debt Instrument [Line Items]      
Debt Instrument, stated interest rate 5.00% 5.00%  
Debt Instrument, Maturity Date, Description   2022  
3.8% Senior Notes due 2024      
Debt Instrument [Line Items]      
Debt Instrument, stated interest rate 3.80% 3.80%  
Debt Instrument, Maturity Date, Description   2024  
4.375% Senior Notes Due 2028      
Debt Instrument [Line Items]      
Debt Instrument, stated interest rate 4.375% 4.375%  
Debt Instrument, Maturity Date, Description   2028  
4.9% Senior Notes due 2044      
Debt Instrument [Line Items]      
Debt Instrument, stated interest rate 4.90% 4.90%  
Debt Instrument, Maturity Date, Description   2044  
Estimated Fair Value      
Debt Instrument [Line Items]      
Credit facility $ 0 $ 0 188,000
Notes Payable 8,800 8,800 9,900
Estimated Fair Value | 5% Senior Notes due 2022 (1)      
Debt Instrument [Line Items]      
Senior notes 2,030,100 2,030,100 2,040,000
Estimated Fair Value | 3.8% Senior Notes due 2024      
Debt Instrument [Line Items]      
Senior notes 976,000 976,000 988,800
Estimated Fair Value | 4.375% Senior Notes Due 2028      
Debt Instrument [Line Items]      
Senior notes 994,100 994,100 987,200
Estimated Fair Value | 4.9% Senior Notes due 2044      
Debt Instrument [Line Items]      
Senior notes 683,600 683,600 679,900
Carrying Amount      
Debt Instrument [Line Items]      
Credit facility 0 0 188,000
Notes Payable 8,845 8,845 9,974
Carrying Amount | 5% Senior Notes due 2022 (1)      
Debt Instrument [Line Items]      
Senior notes 1,997,782 1,997,782 1,997,576
Carrying Amount | 3.8% Senior Notes due 2024      
Debt Instrument [Line Items]      
Senior notes 992,588 992,588 992,036
Carrying Amount | 4.375% Senior Notes Due 2028      
Debt Instrument [Line Items]      
Senior notes 988,090 988,090 988,061
Carrying Amount | 4.9% Senior Notes due 2044      
Debt Instrument [Line Items]      
Senior notes $ 691,435 $ 691,435 $ 691,354