EXHIBIT 2

JOINT FILING AGREEMENT

The undersigned hereby agree to the joint filing of the Amendment No. 4 to Schedule 13D to which this Agreement is attached.

Dated:  May 8, 2015

DISCOVERY GROUP I, LLC,
for itself and as general partner of
DISCOVERY EQUITY PARTNERS, L.P.
By	Michael R. Murphy*
	Michael R. Murphy
	Managing Member
Daniel J. Donoghue*
Daniel J. Donoghue
Michael R. Murphy*
Michael R. Murphy
*By:	/s/ Mark Buckley
	Mark Buckley
	Attorney-in-Fact for Daniel J. Donoghue
	Attorney-in-Fact for Michael R. Murphy