Unaudited Condensed Consolidated Financial Statements - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings		$ 39,921,000	$ 38,980,000	$ 38,348,000
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impact of retrospective guidance in increase to loss from operations and a decrease to other net, other income (expense)	$ 197,000
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings			$ 0