Commitments and contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Commitments And Contingencies [Line Items]
Operating Leases, Rent Expense	$ 1,215,000	$ 830,000
Remediation Costs Incurred		$ 53,000
Officers' Compensation	384,000
Insurance Policy Amount	$ 1,000,000