  Angular correlations between charged trigger and associated particles are
measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon
centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 <
$p_{\rm T}^{\rm assoc}$ < $p_{\rm T}^{\rm trig}$ < 4 GeV/$c$. The correlations
are measured over two units of pseudorapidity and full azimuthal angle in
different intervals of event multiplicity, and expressed as associated yield
per trigger particle. Two long-range ridge-like structures, one on the near
side and one on the away side, are observed when the per-trigger yield obtained
in low-multiplicity events is subtracted from the one in high-multiplicity
events. The excess on the near-side is qualitatively similar to that recently
reported by the CMS collaboration, while the excess on the away-side is
reported for the first time. The two-ridge structure projected onto azimuthal
angle is quantified with the second and third Fourier coefficients as well as
by near-side and away-side yields and widths. The yields on the near side and
on the away side are equal within the uncertainties for all studied event
multiplicity and $p_{\rm T}$ bins, and the widths show no significant evolution
with event multiplicity or $p_{\rm T}$. These findings suggest that the
near-side ridge is accompanied by an essentially identical away-side ridge.
