Customer Lists and Other Identifiable Intangible Assets, Net - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($)
Finite Lived Intangible Assets [Line Items]
Impairment of finite-lived identifiable intangible assets	$ 0
Customer Lists and Other Identifiable Intangible Assets [Member]
Finite Lived Intangible Assets [Line Items]
Amortization expense for 2018	1,800,000
Amortization expense for 2019	1,800,000
Amortization expense for 2020	1,800,000
Amortization expense for 2021	1,800,000
Amortization expense for 2022	$ 1,800,000
Customer Lists and Other Identifiable Intangible Assets [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life	12 years
Customer Lists and Other Identifiable Intangible Assets [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life	20 years