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Goodwill and Intangible Assets - Goodwill (Parenthetical) (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Apr. 29, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 589,099	$ 588,585		$ 199,703
Goodwill related to the sale of business unit	3,115
Goodwill impairment loss	4,862
Data Analytics Solutions Business [Member]
Goodwill [Line Items]
Goodwill related to the sale of business unit	$ 3,115
Newport [Member]
Goodwill [Line Items]
Goodwill		$ 396,027	$ 396,027