Principles of consolidation and basis of presentation - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Net cash provided by operating activities	$ 1,665,000	$ 892,000
Net cash provided by (used in) investing activities	$ 680,000	(1,467,000)
Restatement Adjustment [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Net cash provided by operating activities		317,000
Net cash provided by (used in) investing activities		$ (317,000)