Customer Lists and Other Identifiable Intangible Assets, Net - Other Identifiable Intangible Assets (Detail) - Customer Lists and Other Identifiable Intangible Assets [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Oct. 01, 2017	Jan. 01, 2017
Finite Lived Intangible Assets [Line Items]
Other identifiable intangible assets, cost	$ 25,288	$ 25,288
Less: Accumulated amortization	(8,347)	(6,968)
Total other identifiable intangible assets, net	$ 16,941	$ 18,320	$ 13,262	$ 10,427