Inventrust Properties (IVT) had the highest return between 2012 and 2014 by a mid-cap US stock, returning 1,067,615%.

ASSET	YEARS	% RETURN
Inventrust Properties (IVT)	2012-2014	1,067,615%
ACADIA Pharmaceuticals (ACAD)	2012-2014	2,786.36%
Patrick Industries (PATK)	2012-2014	964.87%
American Airlines (AAL)	2012-2014	936.57%
TG Therapeutics (TGTX)	2012-2014	682.22%
Ambarella (AMBA)	2012-2014	655.89%
Radian (RDN)	2012-2014	608.83%
Addus HomeCare (ADUS)	2012-2014	577.93%
Nexstar Broadcasting (NXST)	2012-2014	571.26%
Travere Therapeutics (TVTX)	2012-2014	544.21%
Saia (SAIA)	2012-2014	542.23%
Acadia Healthcare (ACHC)	2012-2014	523.32%
HCI (HCI)	2012-2014	509.36%
Avis Budget (CAR)	2012-2014	497.57%
Repligen (RGEN)	2012-2014	472.25%
Pilgrims Pride (PPC)	2012-2014	453.88%
Hanesbrands (HBI)	2012-2014	406.42%
Globalstar, Inc Common Stock (GSAT)	2012-2014	391.07%
Axos Financial (AX)	2012-2014	377.95%
CleanSpark (CLSK)	2012-2014	374.36%
Ligand Pharmaceuticals (LGND)	2012-2014	343.41%
Western Alliance Bancorporation (WAL)	2012-2014	338.48%
Jazz Pharmaceuticals (JAZZ)	2012-2014	330.64%
Mueller Water Products (MWA)	2012-2014	330.17%
Marriot Vacations Worldwide (VAC)	2012-2014	328.78%

Mid-cap stocks are treated as having a market cap between $2B and $10B.