The top after-market NYSE gainers Wednesday were K12 Inc, Pall Corp, HFF, Inc, National Bank of Greece and Dole Food Co. The top after-market NYSE losers were Spartech Corp, Halcon Resources Corp, Genesee & Wyoming, Chesapeake Lodging Trust and Nautilus, Inc.

Gainers

K12 Inc. (LRN) shares rallied 12.02 percent to $23.95 in post-market trading. The company swung to the fourth quarter net profit of $1.8 million or $0.05 per share compared to the net loss of $2.8 million or $0.08 per share in the same period last year.

Pall Corp. (PLL) shares climbed 7.87 percent to $62.75 in post-market trading. The company reported fourth quarter adjusted net income of $115.9 million or $0.99 per share, up from $89.7 million or $0.76 per share in the same period last year and also topped Reuters' estimate of $0.77 per share.

HFF, Inc. (HF) shares surged 5.10 percent to $15.46 in post-market trading. The company will replace Stratasys, Inc. in the S&P SmallCap 600 index after the close of trading on Tuesday, September 18.

National Bank of Greece SA (NBG) gained 2.68 percent to $2.68 in post-market trading after climbing more than 16 percent in regular trading.

Dole Food Co, Inc. (DOLE) advanced 2.56 percent to $14.43 in post-market trading. The company announced in response to market rumors that it was in advanced negotiations with ITOCHU Corporation for the possible sale of its Packaged Foods and Asia Fresh businesses. No definitive agreements have been signed at this time, and Dole continues in discussions with several other parties regarding these assets and others.

Losers

Spartech Corp. (SEH) shares slumped 7.10 percent to $5.10 in post-market trading. The company reported the third quarter adjusted net profit of $2.5 million or $0.08 per share, down from $3.1 million or $0.10 per share in the same period last year and also fell short of Reuters' estimate of $0.12 per share.

Halcon Resources Corp. (HK) shares plunged 4.22 percent to $7.26 in post-market trading. The company announced the pricing of an underwritten secondary offering of 35,000,000 shares of its common stock offered by EnCap Energy Capital Fund VIII L.P.

Genesee & Wyoming, Inc. (GWR) shares plunged 4 percent to $65.20 in post-market trading. The company announced Wednesday the commencement of the registered underwritten public offerings of the company's Class A Common Stock and tangible equity units.

Chesapeake Lodging Trust (CHSP) declined 2.90 percent to $18.44 in post-market trading. The company announced Wednesday that it was commencing an underwritten public offering of 5,500,000 common shares.

Nautilus, Inc. (NLS) shares fell 2.36 percent to $2.48 in post-market trading.