Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

Stocks got off to a quiet start to the trading week, but Crosstex Energy (ENLC 1.25%) and its affiliated master limited partnership Crosstex Energy (NASDAQ: XTEX) posted huge gains, along with Horizon Pharma (HZNP) and WebMD Health (WBMD). Let's take a closer look at what made those stocks do so much better than the overall stock market, which closed the day around the unchanged level in the absence of major market-moving news.

For investors in the two Crosstex Energy general-partnership and limited-partnership entities, news that Crosstex would join Devon Energy (DVN -0.89%) in creating a new combined set of MLP businesses sent shares soaring. Under the deal, Devon and Crosstex will contribute assets to form the combined businesses, which will have the same general-partner/limited-partner structure that Crosstex currently has. Crosstex general-partnership investors enjoyed a 71% jump in the price of their shares, while Crosstex Energy unitholders saw their investment climb a more modest 33%. After the proposed deal, Crosstex Energy general-partnership shareholders will own 30% of the new general-partnership entity, while Crosstex Energy unitholders will own 40% of the new master-limited partnership's units.

Horizon Pharma gained almost 16% after announcing this morning that its RAYOS delayed-release prednisone tablets would be the subject of two presentations at a rheumatology conference in San Diego later this month. Horizon began its commercial launch of RAYOS earlier this year, and with the two presentations discussing abstracts connected with its use in rheumatoid arthritis patients, the company hopes that the exposure will help it with its marketing efforts.

WebMD Health gained more than 10% as it announced that it would buy out activist Carl Icahn's stake in company. Icahn will receive $177 million for the 5.5 million share position in WebMD Health, working out to $32.08 per share. WebMD Health noted that the transaction won't use up existing share-buyback authorizations, leaving room for it to continue its extensive conventional buyback activity over the past year.