The top after-market NYSE gainers on Monday are: Nautilus, KKR & Co, Stryker, Lennar and GATX. The top after-market NYSE losers on Monday are: The St. Joe Co, CBIZ, Headwaters, Advanced Micro Devices, MarkWest Energy and Alcoa.

Gainers

Nautilus, Inc. (NYSE:NLS) shares advanced 4.46 percent to $2.34 in afterhours trading session on Monday. The stock has a 52 week low of $1.25 and 52 week high of $4.40 and has 68.87M market capitalization.

KKR & Co. L.P. (NYSE:KKR) shares advanced 4.04 percent to $15.70 in post market trading session. Citigroup raised KKR’s price tag to $22.00, from $21.00.

Stryker Corp. (NYSE:SYK) advanced 3.18 percent to $56.44 in aftermarket trading hours. The company forecasts adjusted earnings in 2011 of as much as $3.73 per share against analysts estimation of $3.65 per share.

Lennar Corp (NYSE:LEN) shares advanced 2.70 percent to $19.41 in post market trading session. The company is expected to report fourth quarter net income of $0.02 per share before the markets open on Tuesday.

GATX Corp (NYSE:GMT) shares gained 2.27 percent to $34.74 in aftermarket trading hours. The stock has a 52 week low of $25.40 and 52 week high of $36.93 and has 46.30M outstanding shares.

Losers

The St. Joe Co (NYSE:JOE) shares plunged 9.75 percent to $20.82 in aftermarket trading after the Florida-based real estate developer disclosed it's the subject of an informal inquiry by the Securities and Exchange Commission.

CBIZ, Inc. (NYSE:CBZ) shares declined 5.04 percent to $6.40 in aftermarket trading session. The stock has a 52 week low of $5.20 and 52 week high of $7.55 and has 49.46M outstanding shares.

Headwaters Inc. (NYSE:HW) shares declined 4.44 percent to $5.17 in post market trading session.

Advanced Micro Devices, Inc. (NYSE:AMD) shares declined 4.35 percent to $8.79 in post market trading after announced that the company's President and CEO Dirk Meyer has resigned and that Thomas Seifert has been named Interim CEO.

MarkWest Energy Partners, LP (NYSE:MWE) shares declined 2.25 percent to $41.73 in post market trading hours. The company announced that it is commencing a public offering of 3,000,000 common units.

Alcoa Inc. (NYSE:AA) shares declined 1.70 percent to $16.21 in aftermarket trading session. The company posted better-than-expected fourth quarter net income of $0.21 per share, but sales of $5.65 billion missed $5.71 billlion analysts estimated.