Debt (Detail) - Borrowings - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, gross	$ 702,500,000	$ 825,000,000
Less: deferred financing fees	(8,109,000)	(6,169,000)
Long-term debt	694,391,000	818,831,000
Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt, gross	115,000,000	440,000,000
Term loan
Debt Instrument [Line Items]
Long-term debt, gross	585,000,000	380,000,000
Connecticut Economic Development Program
Debt Instrument [Line Items]
Long-term debt, gross	$ 2,500,000	$ 5,000,000