Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Debt (Details)			1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
Debt (Details)	Apr. 05, 2017 USD ($) amendment installment	Mar. 30, 2017 USD ($)	Jan. 31, 2018 USD ($)	Jun. 30, 2017	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt, gross						$ 3,323,062,000	$ 702,500,000
Debt instrument, interest rate at period end						3.91%
Long-term Debt, Fiscal Year Maturity [Abstract]
2018						$ 80,000,000
2019						107,600,000
2020						144,700,000
2021						42,600,000
2022						1,680,000,000
Thereafter						1,270,000,000
Payments of deferred financing fees						51,171,000	4,975,000	$ 0
Write off of deferred financing fees					$ 6,100,000
Contract notional amount						2,086,764,000	786,946,000
Interest rate swap
Long-term Debt, Fiscal Year Maturity [Abstract]
Contract notional amount						$ 1,400,000,000
Derivative, term of contract						30 days
Interest rate derivative hedge, asset (liability), net						$ 3,400,000	(2,300,000)
Minimum \| Interest rate swap
Long-term Debt, Fiscal Year Maturity [Abstract]
Derivative, fixed interest rate						1.54%
Maximum \| Interest rate swap
Long-term Debt, Fiscal Year Maturity [Abstract]
Derivative, fixed interest rate						2.13%
CEB
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 2,800,000,000
CEB \| Bridge Loan
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 300,000,000
Debt instrument term	364 days			364 days
Repayments of short-term debt						$ 300,000,000
Term loan
Debt Instrument [Line Items]
Interest rate at period end						3.57%
Debt instrument, interest base rate						1.57%
Debt instrument, interest, additional interest above base rate						2.00%
Long-term debt, gross						$ 1,429,312,000	585,000,000
Term B facility
Debt Instrument [Line Items]
Long-term debt, gross						496,250,000	0
Senior notes
Debt Instrument [Line Items]
Proceeds from issuance of debt		$ 800,000,000
Long-term debt, gross						800,000,000	0
Senior notes \| CEB
Debt Instrument [Line Items]
Proceeds from issuance of debt		$ 800,000,000
Debt instrument term		8 years
Debt instrument, fixed interest rate		5.125%
Issue price, percent		100.00%
Redeemable percentage of principal amount		40.00%
Senior notes \| CEB \| Redemption period one
Debt Instrument [Line Items]
Redemption price percentage		105.125%
Senior notes \| CEB \| Redemption period two
Debt Instrument [Line Items]
Redemption price percentage		100.00%
Senior notes \| CEB \| Redemption period three
Debt Instrument [Line Items]
Redemption price percentage		101.00%
Connecticut Economic Development Program
Debt Instrument [Line Items]
Debt instrument term									10 years
Debt instrument, fixed interest rate									3.00%
Long-term debt, gross						2,500,000	2,500,000
Principal amount outstanding						$ 2,500,000
Period principal payments term									5 years
Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate at period end						4.07%
Floating eurodollar base rate						1.57%
Additional interest above base rate						2.50%
Line of credit facility, remaining borrowing capacity						$ 558,000,000
Long-term debt, gross						$ 595,000,000	$ 115,000,000
Revolving Credit Facility \| Subsequent Event
Long-term Debt, Fiscal Year Maturity [Abstract]
Repayments of lines of credit			$ 255,000,000
Revolving Credit Facility \| CEB
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 275,000,000
Revolving Credit Facility \| Term B facility
Debt Instrument [Line Items]
Interest rate at period end						2.23%
2016 Credit Facility Agreement
Debt Instrument [Line Items]
Number of debt agreement amendments \| amendment	3
Debt instrument, interest, additional interest above eurodollar rate	1.00%
2016 Credit Facility Agreement \| Federal Funds rate
Debt Instrument [Line Items]
Minimum applicable margin rate	0.125%
Maximum applicable margin rate	1.50%
2016 Credit Facility Agreement \| Euro Dollar rate
Debt Instrument [Line Items]
Minimum applicable margin rate	1.125%
Maximum applicable margin rate	2.50%
2016 Credit Facility Agreement \| CEB
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 1,675,000,000
2016 Credit Facility Agreement \| Secured Debt
Debt Instrument [Line Items]
Line of credit facility, frequency of payments in quarterly installments \| installment	16
2016 Credit Facility Agreement \| Secured Debt \| Term loan
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 1,500,000,000
2016 Credit Facility Agreement \| Secured Debt \| Term loan \| CEB
Debt Instrument [Line Items]
Additional borrowing capacity	$ 900,000,000
2016 Credit Facility Agreement \| Secured Debt \| Term B facility \| CEB
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						500,000,000
Proceeds from issuance of debt	$ 500,000,000
2016 Credit Facility Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 1,200,000,000
Federal Funds rate
Debt Instrument [Line Items]
Additional interest above federal fund rate						0.50%
Term B facility \| Secured Debt \| CEB \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Term B facility \| Secured Debt \| CEB \| Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%