Debt (Detail) (USD $)	3 Months Ended		1 Months Ended	12 Months Ended
	Mar. 31, 2015		Feb. 28, 2015	Dec. 31, 2012	Dec. 31, 2014
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,500,000,000.0
Line of credit facility, additional borrowing capacity	500,000,000.0
Debt Instrument, interest, additional interest above eurodollar rate	1.00%
Line of credit facility, remaining borrowing capacity	831,800,000
Debt instrument, interest rate at period end	2.50%
Notional amount of interest rate derivatives	410,000,000				245,650,000
Letters of credit outstanding, amount	7,700,000
Interest rate swap
Debt Instrument [Line Items]
Derivative, fixed interest rate	2.26%		1.60%
Notional amount of interest rate derivatives	200,000,000		200,000,000
Derivative, term of contract	90 days		30 days
Interest rate, fair value hedge derivative at fair value, net (negative fair value)	4,700,000
Federal Funds rate
Debt Instrument [Line Items]
Debt instrument, interest, additional interest above federal fund rate	0.50%
Term loans
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	400,000,000
Debt instruments, maturity duration	5 years
Line of credit facility, frequency of payments	16
Debt instrument, interest, additional interest above base rate	1.25%
Revolver loans
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,100,000,000.0
Revolver loans | Letter of credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	40,000,000.0
Connecticut Economic Development Program
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				5,000,000.0
Debt instrument, period principal payments are deferred				5 years
Debt instrument, maturity period				10 years
Debt instrument, fixed interest rate				3.00%
Line of credit facility, decrease, forgiveness				$ 2,500,000.0
Debt instrument, forgiveness period under the terms of the loan				5 years
Minimum
Debt Instrument [Line Items]
Floating eurodollar based rate	0.18%
Minimum | Term loans
Debt Instrument [Line Items]
Contractual annualized interest rate	1.43%	[1]
Maximum
Debt Instrument [Line Items]
Floating eurodollar based rate	0.28%
Maximum | Term loans
Debt Instrument [Line Items]
Contractual annualized interest rate	1.53%	[1]
Euro Dollar rate
Debt Instrument [Line Items]
Minimum applicable margin rate	1.125%
Maximum applicable margin rate	1.50%
Euro Dollar rate | Federal Funds rate
Debt Instrument [Line Items]
Minimum applicable margin rate	0.125%
Maximum applicable margin rate	0.50%

[1] The contractual annualized interest rates as of March 31, 2015 on the term loan and the revolver ranged from 1.43% to 1.53%, which consisted of a floating eurodollar base rate ranging from 0.18% to 0.28% plus a margin of 1.25%. However, the Company has two interest rate swap contracts which convert the floating eurodollar base rates to a fixed base rate on the first $400.0 million of Company borrowings (see below).