Biogen Idec (Nasdaq: BIIB) can do no wrong. Well, almost no wrong.

After posting stellar phase 3 data for its oral multiple sclerosis drug BG-12 in the middle of last week, the biotech followed up with a solid earnings report Friday.

Revenue up 11%, adjusted EPS up 19% -- who can argue with that?

Biogen's current multiple sclerosis drugs are doing great. Revenue from Tysabri, which it sells with Elan (NYSE: ELN), were up 26%, while its older medication Avonex was up a solid-enough 6%.

Biogen's cut of cancer drug Rituxan, which Roche sells, was up 3%, but that's becoming an increasingly smaller part of Biogen's growth story. Tysabri trumped Rituxan this quarter, putting Rituxan third on the revenue contribution list.

When BG-12 gets to market, Biogen will have a full complement of multiple sclerosis drugs. BG-12 will likely cut into Avonex sales, but that's an acceptable sacrifice because it'll also take sales away from other injectable drugs such as Teva Pharmaceuticals' (Nasdaq: TEVA) Copaxone, and Rebif from Merck KGaA and Pfizer (NYSE: PFE). Tysabri, which is typically used later because of potential side effects, probably won't be affected that much. The big competition will come from Novartis' (NYSE: NVS) oral multiple sclerosis drug Gilenya, but BG-12 seems up to the task.

About the only thing Biogen could have done to impress investors more was up its guidance for the year, which basically means the fourth quarter at this point. Biogen stuck with its adjusted earnings guidance of above $5.70 per share.

My guess is the company figures there's no reason to rock the boat, raising guidance with the risk of not making it. When you're on a good streak, sometimes it's better to just play the conservative card and figure that if you beat next quarter, you'll keep the momentum going.