Treasury - Additional Information (Detail) $ in Thousands				3 Months Ended			9 Months Ended		12 Months Ended
	Nov. 26, 2018 USD ($)	Oct. 23, 2018 USD ($)	Jun. 07, 2016 USD ($)	Dec. 31, 2015 USD ($) Derivative	Sep. 30, 2015 USD ($) Derivative	Jun. 30, 2015 USD ($) Derivative	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2015 USD ($) Derivative	Dec. 31, 2018 USD ($)	Oct. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Apr. 30, 2018 USD ($)	Jun. 03, 2016 USD ($)	Aug. 07, 2014 USD ($)
Equity Class Of Treasury Stock [Line Items]
Line of credit facility, starting date							Oct. 23, 2018
Rate adjustment to weighted average federal funds rate for credit facility borrowings							0.50%
Rate adjustment to one month Eurodollar rate on credit facility borrowings							1.00%
Accounts receivable securitization program credit facility, borrowing capacity												$ 440,000	$ 450,000
Accounts receivable securitization program credit facility, amount outstanding							$ 365,000
Accounts receivable securitization program credit facility, available borrowing capacity							85,000
Debt instrument carrying amount							3,950,000			$ 4,000,000
Fair value of debt							3,970,000			$ 4,000,000
Number of additional forward starting interest rate swaps | Derivative					4
One Point Three One Percent Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Number of additional forward starting interest rate swaps | Derivative									9
Maturity date of interest rate cash flow hedges									Apr. 15, 2019
Fixed rate payable on interest rate swap				1.31%					1.31%
One Point Four Zero Percent Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Number of additional forward starting interest rate swaps | Derivative						4,000,000
Maturity date of interest rate cash flow hedges						Apr. 15, 2019
Average fixed rate payable on interest rate swap						1.40%
Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Maturity date of interest rate cash flow hedges					Apr. 15, 2019
Average fixed rate payable on interest rate swap					1.23%
One Point Two One Percent Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Number of additional forward starting interest rate swaps | Derivative				1
Maturity date of interest rate cash flow hedges				Apr. 15, 2019
Fixed rate payable on interest rate swap				1.21%					1.21%
Foreign Currency Forward Exchange Contracts
Equity Class Of Treasury Stock [Line Items]
Net cash inflows (outflows)							90,000	$ 26,000
Cash Flow Hedging | One Point Three One Percent Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges				$ 1,000,000					$ 1,000,000
Cash Flow Hedging | One Point Four Zero Percent Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges						$ 500,000
Cash Flow Hedging | Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges					$ 400,000
Cash Flow Hedging | One Point Two Three Percent Forward Starting Interest Rate Swaps One
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges					100,000
Cash Flow Hedging | One Point Two Three Percent Forward Starting Interest Rate Swaps Two
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges					200,000
Cash Flow Hedging | One Point Two Three Percent Forward Starting Interest Rate Swaps Three
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges					$ 100,000
Cash Flow Hedging | One Point Two One Percent Forward Starting Interest Rate Swaps
Equity Class Of Treasury Stock [Line Items]
Notional amount of interest rate cash flow hedges				$ 100,000					$ 100,000
Revolving Credit Facility
Equity Class Of Treasury Stock [Line Items]
Line of credit facility, borrowing capacity		$ 1,000,000	$ 800,000				1,000,000
Line of credit facility increased amount		200,000
Line of credit facility, available borrowing capacity							967,000
Line of credit facility amount outstanding							$ 0
Current applicable margins							1.50%
Revolving Credit Facility | ABR-based loans
Equity Class Of Treasury Stock [Line Items]
Current applicable margins							1.75%
Revolving Credit Facility | Minimum | One Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							0.375%
Revolving Credit Facility | Minimum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							1.375%
Revolving Credit Facility | Maximum | One Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							0.625%
Revolving Credit Facility | Maximum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							1.625%
Revolving Credit Facility | Short Term on Demand Credit Facility
Equity Class Of Treasury Stock [Line Items]
Line of credit facility amount outstanding							$ 21,000
Revolving Credit Facility | Letter of Credit
Equity Class Of Treasury Stock [Line Items]
Line of credit facility, borrowing capacity							125,000
Line of credit facility amount outstanding							12,000
Tranche A Term Loan
Equity Class Of Treasury Stock [Line Items]
Line of credit facility, borrowing capacity		2,000,000	$ 1,710,000
Line of credit facility increased amount		$ 290,000
Senior notes, maturity date		Oct. 23, 2023	Aug. 07, 2019
Line of credit facility amount outstanding							1,963,000
Tranche A Term Loan | Quarterly Payment for First Eight Installments
Equity Class Of Treasury Stock [Line Items]
Scheduled principal payments per quarter							$ 12,500
Debt Instrument Periodic Payment, description							commenced in March of 2019 and are scheduled to continue through December of 2020
Tranche A Term Loan | Quarterly Payment after Eight Installments Until Maturity
Equity Class Of Treasury Stock [Line Items]
Scheduled principal payments per quarter							$ 25,000
Debt Instrument Periodic Payment, description							commencing in March of 2021 until maturity in October of 2023
Tranche B Term Loan
Equity Class Of Treasury Stock [Line Items]
Line of credit facility, borrowing capacity											$ 500,000
Senior notes, maturity date							Oct. 31, 2025
Line of credit facility amount outstanding							$ 496,000
Scheduled principal payments per quarter							$ 1,250
Debt Instrument Periodic Payment, description							which commenced on March 31, 2019 and are scheduled to continue until maturity in October of 2025
New Senior Secured Notes
Equity Class Of Treasury Stock [Line Items]
Senior notes, issued							$ 1,100,000
New Senior Secured Notes | 3.75% Senior Secured Notes due 2019
Equity Class Of Treasury Stock [Line Items]
Senior Notes															$ 300,000
Senior notes, interest rate															3.75%
Redemption of senior notes	$ 300,000
Redemption price, percentage	100.485%
Redemption premium paid	$ 1,000
New Senior Secured Notes | 4.75% Senior Secured Notes due 2022
Equity Class Of Treasury Stock [Line Items]
Senior notes, maturity date							Aug. 01, 2022
Senior notes, interest rate							4.75%
Senior notes, issued							$ 700,000
New Senior Secured Notes | 4.75% Senior Secured Notes due 2022 | Senior Secured Notes Issued on August Seven Two Thousand Fourteen
Equity Class Of Treasury Stock [Line Items]
Senior notes, issued							300,000
New Senior Secured Notes | 4.75% Senior Secured Notes due 2022 | Senior Secured Notes Issued on June Three Two Thousand Sixteen
Equity Class Of Treasury Stock [Line Items]
Senior notes, issued							$ 400,000
Senior notes issued percentage							101.50%
Senior notes yield percentage							4.35%
New Senior Secured Notes | 5.00% Senior Secured Notes due 2026
Equity Class Of Treasury Stock [Line Items]
Senior notes, maturity date							Jun. 01, 2026
New Senior Secured Notes | 5.00% Senior Secured Notes due 2026 | Senior Secured Notes Issued on June Three Two Thousand Sixteen
Equity Class Of Treasury Stock [Line Items]
Senior notes, interest rate														5.00%
Senior notes, issued														$ 400,000
Term Loan A
Equity Class Of Treasury Stock [Line Items]
Current applicable margins							1.50%
Term Loan A | ABR-based loans
Equity Class Of Treasury Stock [Line Items]
Current applicable margins							0.50%
Term Loan A | Minimum | One Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							0.375%
Term Loan A | Minimum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							1.375%
Term Loan A | Maximum | One Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							0.625%
Term Loan A | Maximum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							1.625%
Term Loan A | Tranche B Term Loan | One Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							0.75%
Term Loan A | Tranche B Term Loan | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Equity Class Of Treasury Stock [Line Items]
Consolidated Leverage Ratio							1.75%