Goodwill and Other Intangible Assets - Summary of Gross Amounts and Accumulated Amortization of Identifiable Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 24,925	$ 24,925
Accumulated Amortization	13,003	11,632
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	19,000	19,000
Accumulated Amortization	8,502	7,439
Covenants not-to-Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	4,425	4,425
Accumulated Amortization	4,209	4,001
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Amount	1,500	1,500
Accumulated Amortization	$ 292	$ 192