Note 15 - Commitments and Contingencies (Details Textual)		1 Months Ended	12 Months Ended
	Mar. 01, 2013	Aug. 31, 2015 ft²	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jul. 31, 2015 ft²
Number of Non-cancelable Operating Leases			6
Number of Laboratories Acquired			2
Operating Leases, Rent Expense			$ 1,400,000	$ 900,000	$ 700,000
Corporate Headquarters [Member]
Lessee Leasing Arrangements, Operating Leases, Term of Contract	5 years
Office Space in Malborough, Massachusetts [Member]
Lessee Leasing Arrangements, Operating Leases, Renewal Term		2 years
Area of Leased Space | ft²		22,100				7,600
Lessee Leasing Arrangements, Operating Leases, Optional Extension of Contract			5 years
Office Space in Malborough, Massachusetts [Member] | Office Expansion [Member]
Operating Leases, Rent Expense, Per Month				12,000
Office Space in Malborough, Massachusetts [Member] | Minimum [Member]
Operating Leases, Rent Expense, Per Month				36,000
Office Space in Malborough, Massachusetts [Member] | Maximum [Member]
Operating Leases, Rent Expense, Per Month				$ 39,000
Laboratory Space in Memphis, Tennessee [Member]
Lessee Leasing Arrangements, Operating Leases, Optional Extension of Contract			5 years
Norwood Lease [Member]
Area of Leased Space | ft²			22,000
Operating Leases, Rent Expense			$ 412,000
Boston Lease [Member]
Area of Leased Space | ft²			18,000
Operating Leases, Rent Expense			$ 263,000