Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]
Accumulated goodwill impairment losses	$ 0
Amortization of intangible assets	781,000	$ 831,000	$ 891,000
Remaining net book value	$ 732,000	$ 1,464,000