Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Goodwill accumulated impairment loss	$ 0
Intangible assets, Amortization expense	$ 3,900,000	$ 1,300,000
Hub [Member] | Weighted Average [Member]
Intangible Assets [Line Items]
Weighted average life of definite lived intangible assets	14 years 3 months 29 days
Mode [Member] | Weighted Average [Member]
Intangible Assets [Line Items]
Weighted average life of definite lived intangible assets	11 years 3 months