NEW YORK (AP) — Biogen Idec Inc. backed its $356 million buyout offer for Facet Biotech Tuesday afternoon, hours after Facet turned Biogen Idec down. The Cambridge, Mass.-based company said its offer for Facet, which totals $14.50 per share, is "extremely attractive" and fairly values Facet's pipeline of drug candidates. Biogen Idec made its bid late Friday, and Tuesday morning, Facet said it undervalued the company. Facet shares closed at $8.82 before Biogen made its unsolicited offer. But the stock finished up 5 percent at $16.15 on Tuesday, which suggests investors are expecting a sweeter offer. Facet, based in Redwood City, Calif., has been working with Biogen for the last four years on a pair of drugs: volociximab for cancer, and daclizumab for multiple sclerosis.