Business Combinations - Additional Information (Detail) £ in Millions			12 Months Ended
	Jun. 01, 2015 GBP (£)	Jun. 01, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Business combination, aggregate purchase price			$ 49,400,000	$ 59,400,000
Goodwill			924,847,000	$ 897,933,000
dlc [Member]
Business Acquisition [Line Items]
Business combination, aggregate purchase price	£ 180.6	$ 274,700,000
Revenue included in condensed consolidated statement of income			27,500,000
Net income included in condensed consolidated statement of income			6,300,000
Goodwill		$ 66,486,000
Amount of goodwill expected to be tax deductible			$ 0
Baycorp [Member]
Business Acquisition [Line Items]
Noncontrolling interest, ownership percentage			50.25%
Fair value of total assets acquired			$ 76,100,000
General and Administrative Expense [Member] | dlc [Member]
Business Acquisition [Line Items]
Acquisition and integration costs			$ 2,800,000