Components of Other Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Other Intangible Assets [Line Items]
Finite-lived intangible assets, Accumulated Amortization	$ (12,595)	$ (8,699)
Intangible Assets, Gross Amount	86,943	20,543
Intangible Assets, Net Carrying Value	74,348	11,844
Hub [Member] | Customer Relationships [Member]
Other Intangible Assets [Line Items]
Finite-lived intangible assets, Gross Amount	71,181	5,181
Finite-lived intangible assets, Accumulated Amortization	(6,434)	(3,792)
Finite-lived intangible assets, Net Carrying Value	$ 64,747	$ 1,389
Hub [Member] | Customer Relationships [Member] | Minimum [Member]
Other Intangible Assets [Line Items]
Intangible assets estimated useful life	7 years	7 years
Hub [Member] | Customer Relationships [Member] | Maximum [Member]
Other Intangible Assets [Line Items]
Intangible assets estimated useful life	15 years	15 years
Hub [Member] | Trade Name [Member]
Other Intangible Assets [Line Items]
Finite-lived intangible assets, Gross Amount	$ 400
Finite-lived intangible assets, Accumulated Amortization	$ (400)
Intangible assets estimated useful life	3 months
Mode [Member] | Agency/Customer Relationships [Member]
Other Intangible Assets [Line Items]
Finite-lived intangible assets, Gross Amount	$ 15,362	$ 15,362
Finite-lived intangible assets, Accumulated Amortization	(5,761)	(4,907)
Finite-lived intangible assets, Net Carrying Value	$ 9,601	$ 10,455
Intangible assets estimated useful life	18 years	18 years