Debt (Detail) - Borrowings	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) contract outstanding_contract	Dec. 31, 2012 USD ($)	Jun. 17, 2016 USD ($)	Dec. 31, 2015 USD ($) outstanding_contract
Debt Instrument [Line Items]
Long-term debt, gross		$ 745,000,000			$ 825,000,000
Debt issuance costs, line of credit arrangements, net		(8,595,000)			0
Long-term debt		$ 736,405,000			825,000,000
Debt instrument interest additional interest above base rate		1.38%
Notional amount of interest rate derivatives		$ 723,089,000			$ 893,610,000
Debt instrument, effective percentage		2.77%
Number of derivative contracts | outstanding_contract		19			105
Interest rate swap
Debt Instrument [Line Items]
Notional amount of interest rate derivatives		$ 700,000,000
Number of derivative contracts | contract		3
Derivative, term of contract		30 days
Interest rate, fair value hedge derivative at fair value, net (negative fair value)		$ 14,900,000
Interest rate swap | Minimum
Debt Instrument [Line Items]
Derivative, fixed interest rate		1.53%
Interest rate swap | Maximum
Debt Instrument [Line Items]
Derivative, fixed interest rate		1.60%
2016 Credit Facility Agreement
Debt Instrument [Line Items]
Debt issuance costs, gross		$ 5,000,000		$ 5,000,000
Bank Term Loan
Debt Instrument [Line Items]
Long-term debt, gross		$ 592,500,000			$ 380,000,000
Long-term debt				$ 600,000,000
Contractual annualized interest rate		1.90%
Floating eurodollar based rate		0.52%
Bank Term Loan | Interest rate swap
Debt Instrument [Line Items]
Notional amount of interest rate derivatives		$ 700,000,000
Connecticut Economic Development Program
Debt Instrument [Line Items]
Long-term debt, gross		5,000,000			5,000,000
Debt instrument, fixed interest rate			3.00%
Debt instrument term			10 years
Debt instrument, period principal payments are deferred			5 years
Debt instrument, principal forgiveness provision			$ 2,500,000.0
Debt instrument, forgiveness period under the terms of the loan			5 years
Revolving credit facility
Debt Instrument [Line Items]
Long-term debt, gross		$ 147,500,000			$ 440,000,000
Contractual annualized interest rate		1.84%
Line of credit facility, remaining borrowing capacity		$ 1,050,000,000
Letter of Credit
Debt Instrument [Line Items]
Letters of credit outstanding, amount		$ 3,800,000
Scenario, Forecast | Connecticut Economic Development Program
Debt Instrument [Line Items]
Debt instrument, decrease, forgiveness	$ 2,500,000.0