Interest rates on Debentures issued (Details)	Mar. 31, 2014
Interest rates on Debentures issued
Variable rate of interest on 2033 Debentures	3.49%
Variable rate of interest on 2034 Debentures	3.04%
Variable rate of interest on 2036 Debentures	1.56%
LIBOR plus Variable rate of interest on 2033 Debentures	3.25%
LIBOR plus Variable rate of interest on 2034 Debentures	2.80%
LIBOR plus Variable rate of interest on 2036 Debentures	1.33%