Goodwill and Intangible Assets - Summary of the Identifiable Intangible Assets Subject for Amortization (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 24,117	$ 24,117
Impairment Charges	0	0
Accumulated Amortization	18,542	15,739
Net Carrying Amount	5,575	8,378
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	22,978	22,978
Impairment Charges	0	0
Accumulated Amortization	17,403	14,611
Net Carrying Amount	5,575	8,367
Capitalized Product Development Costs [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,139	1,139
Impairment Charges	0	0
Accumulated Amortization	$ 1,139	1,128
Net Carrying Amount		$ 11