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Long-Term Debt - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Apr. 30, 2018
Apr. 09, 2018
Dec. 31, 2017
Debt Instrument [Line Items]        
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net $ 43,400     $ 44,300
Line of credit facility, maturity date May 16, 2019      
Aggregate amount of lender commitments on credit facility $ 2,750,000      
Line of credit facility, commitment fee percentage, per annum 0.20%      
Current portion of long-term debt $ 2,304     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%      
Debt Instrument, Maturity Date, Description 2023      
Note payable        
Debt Instrument [Line Items]        
Notes Payable $ 22,000      
Loan term 10 years      
Debt Instrument, stated interest rate 3.14%      
Debt Instrument, Maturity Date Feb. 26, 2022      
5% Senior Notes due 2022        
Debt Instrument [Line Items]        
Debt Instrument, stated interest rate 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%      
Debt Instrument, Maturity Date, Description 2024      
4.375% Senior Notes Due 2028        
Debt Instrument [Line Items]        
Debt Instrument, stated interest rate 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%      
Debt Instrument, Maturity Date, Description 2044      
Estimated Fair Value        
Debt Instrument [Line Items]        
Credit facility $ 0     188,000
Notes Payable 9,300     9,900
Estimated Fair Value | 5% Senior Notes due 2022        
Debt Instrument [Line Items]        
Senior notes 2,032,500     2,040,000
Estimated Fair Value | 3.8% Senior Notes due 2024        
Debt Instrument [Line Items]        
Senior notes 964,200     988,800
Estimated Fair Value | 4.375% Senior Notes Due 2028        
Debt Instrument [Line Items]        
Senior notes 976,200     987,200
Estimated Fair Value | 4.9% Senior Notes due 2044        
Debt Instrument [Line Items]        
Senior notes 668,900     679,900
Carrying Amount        
Debt Instrument [Line Items]        
Credit facility 0     188,000
Notes Payable 9,411     9,974
Carrying Amount | 5% Senior Notes due 2022        
Debt Instrument [Line Items]        
Senior notes 1,997,678     1,997,576
Carrying Amount | 3.8% Senior Notes due 2024        
Debt Instrument [Line Items]        
Senior notes 992,311     992,036
Carrying Amount | 4.375% Senior Notes Due 2028        
Debt Instrument [Line Items]        
Senior notes 988,045     988,061
Carrying Amount | 4.9% Senior Notes due 2044        
Debt Instrument [Line Items]        
Senior notes $ 691,394     $ 691,354
Subsequent Event [Member]        
Debt Instrument [Line Items]        
Credit facility   $ 0    
Aggregate amount of lender commitments on credit facility     $ 1,500,000  
Line of Credit Facility, Maximum Borrowing Capacity     $ 4,000,000