Commitments and contingencies (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($)
Auburn, Washington
Rent Expense [Line Items]
Rent expense	$ 51,000
Lease Expiration Date	Aug. 31, 2018
Baton Rouge, Louisiana
Rent Expense [Line Items]
Rent expense	$ 15,000
Lease Expiration Date	Apr. 30, 2017
Trousdale, Tennessee
Rent Expense [Line Items]
Rent expense	$ 36,000
Lease Expiration Date	Mar. 31, 2016
Champaign, Illinois
Rent Expense [Line Items]
Rent expense	$ 457,000
Lease Expiration Date	Dec. 31, 2017
Charlotte, North Carolina
Rent Expense [Line Items]
Rent expense	$ 63,000
Lease Expiration Date	Mar. 31, 2016
Escondido, California
Rent Expense [Line Items]
Rent expense	$ 36,000
Lease Expiration Period Description	Month to Month
Hampstead, New Hampshire
Rent Expense [Line Items]
Rent expense	$ 28,000
Lease Expiration Date	Aug. 31, 2017
Nashville, Tennessee
Rent Expense [Line Items]
Rent expense	$ 162,000
Lease Expiration Date	Mar. 31, 2018
Ontario, California
Rent Expense [Line Items]
Rent expense	$ 87,000
Lease Expiration Date	Dec. 31, 2018
Pearl River, New York
Rent Expense [Line Items]
Rent expense	$ 93,000
Lease Expiration Date	Aug. 31, 2018
Pottsboro, Texas
Rent Expense [Line Items]
Rent expense	$ 9,600
Lease Expiration Date	Aug. 31, 2017
San Juan, Puerto Rico
Rent Expense [Line Items]
Rent expense	$ 151,000
Lease Expiration Date	Nov. 30, 2020
Stony Point, New York
Rent Expense [Line Items]
Rent expense	$ 117,000
Lease Expiration Date	Jun. 30, 2016
Tulsa, Oklahoma
Rent Expense [Line Items]
Rent expense	$ 27,000
Lease Expiration Date	Dec. 31, 2017