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.

Markets were red across the board today. Three in four stocks fell, and all 10 market sectors posted losses. You'd think someone had accidentally fired a nuke, judging by the pessimism on Wall Street. Thankfully, no nukes were fired. Today's sell-off was merely the result of impressive third-quarter GDP growth.

Wait... what?

Yes, the days of Wall Street's counterintuitive rationale are still among us, if anyone was wondering. Unexpected strength in the U.S. economy, such as today's data showing 2.8% GDP growth in the third quarter, is perceived as a threat to the Federal Reserve's loose money policies. The Fed currently pumps $85 billion per month into the country through various asset purchases. Fearing the central bank will wean that figure in coming months, the S&P 500 Index (SNPINDEX:^GSPC) dropped 23 points, or 1.3%, to end at 1,747. 

Shares of International Game Technology (NYSE:IGT), which develops casino-style games, slumped 12.4% Thursday on the heels of its quarterly report. Earnings slumped more than 20%, missing Wall Street estimates, as slot machines fell out of favor. While IGT's online gaming property Double Down saw revenue jump more than 70%, overall revenue was up just 1% in the most recent period. The silver lining to the disappointing announcement is that IGT approved an accelerated $200 million share buyback, so it looks like the gaming company is betting on its own stock. 

Stock in aluminum giant Alcoa (NYSE:AA) fell 7.4% Thursday, as the London Metal Exchange, or LME, implemented strict new rules to prevent bottlenecking in the flow of materials to endusers. The LME has grown increasingly critical of warehousing trends in the metals market, accusing producers like Alcoa of stockpiling reserves in order to limit supply, and drive up metals prices. Alcoa, despite having spoken out vehemently against similar proposed regulations before, refrained itself from making an impassioned response to the rules today. 

Finally, telecom services company CenturyLink (NYSE:CTL) dropped 6.1% after an underwhelming quarterly report yesterday. Let's start with the positives: CenturyLink met earnings estimates, and slightly beat on revenue for the third quarter. As for the negatives, the company wrote down $1.1 billion worth of goodwill in its data housing business on weaker-than-expected growth. Goodwill, as you may expect from the name, is an intangible asset, and therefore difficult for investors to get a good feel for. Write-downs like today's tell investors that the company overpaid for an acquisition at some point in the past, as CenturyLink is admitting to having done with its multibillion-dollar deal to acquire SAVVIS in 2011.