Goodwill and Other Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 32,818	$ 32,081
Accumulated Amortization	32,086	30,617
Total	732	1,464
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	31,735	30,998
Accumulated Amortization	31,003	29,534
Total	732	1,464
Research Content [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,083	1,083
Accumulated Amortization	$ 1,083	$ 1,083