We study a class of algebras B(n,l) associated with integrable models with boundaries. These algebras can be identified with coideal subalgebras in the Yangian for gl(n). We construct an analog of the quantum determinant and show that its coefficients generate the center of B(n,l). We develop an analog of Drinfeld's highest weight theory for these algebras and give a complete description of their finite-dimensional irreducible representations.