# Gain and Phase Margins from Bode Plot

What's the interpretation of the margins when the curve of magnitude never crosses 0 dB or the phase curve never crosses the -180º? For example:

$$G(s) = \frac{s+20}{(s+1)(s+7)(s+50)}$$

I know that this TF is stable looking it's pole/zero map. But how I can achieve this information just looking the bode plot, when the margins aren't explicity?