Goodwill Activities and Other Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0
Amortization expense				$ 1,200,000	$ 1,200,000	$ 900,000
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Useful life of intangible asset				5 years
Other [Member]
Finite Lived Intangible Assets [Line Items]
Useful life of intangible asset				3 years
Minimum [Member] | Customer relationships [Member]
Finite Lived Intangible Assets [Line Items]
Useful life of intangible asset				15 years
Maximum [Member] | Customer relationships [Member]
Finite Lived Intangible Assets [Line Items]
Useful life of intangible asset				16 years