Par Pacific (PARR) had the highest return between 2011 and 2012 by a mid-cap US stock, returning 1,900%.

ASSET	YEARS	% RETURN
Par Pacific (PARR)	2011-2012	1,900%
Patrick Industries (PATK)	2011-2012	674.03%
ACADIA Pharmaceuticals (ACAD)	2011-2012	290.76%
Travere Therapeutics (TVTX)	2011-2012	272.22%
Delek US Energy (DK)	2011-2012	262.68%
Astrana Health (ASTH)	2011-2012	257.14%
Acadia Healthcare (ACHC)	2011-2012	243.38%
CVR Energy (CVI)	2011-2012	216.61%
Vipshop (VIPS)	2011-2012	197.34%
Domino's Pizza Inc Common Stock (DPZ)	2011-2012	192.28%
HCI (HCI)	2011-2012	185.89%
PDF Solutions (PDFS)	2011-2012	182.38%
Builders FirstSource (BLDR)	2011-2012	179%
Lithia Motors (LAD)	2011-2012	166.24%
Golar LNG (GLNG)	2011-2012	165.06%
Melco Resorts & Entertainment (MLCO)	2011-2012	156.71%
Fortune Brands Innovations (FBIN)	2011-2012	145.55%
Six Flags Entertainment (FUN)	2011-2012	141.5%
CommVault Systems (CVLT)	2011-2012	141.46%
NewMarket (NEU)	2011-2012	138.38%
SPS Commerce (SPSC)	2011-2012	133.23%
Dillard's (DDS)	2011-2012	132.46%
Ligand Pharmaceuticals (LGND)	2011-2012	131.21%
Stewart Information Services (STC)	2011-2012	125.02%
Boyd Group Services (BGSI)	2011-2012	124.91%

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