Why was Nixon's policy of détente successful?

Nixon's policy of detente was broadly successful. 
Tensions between the US and the Soviet Union eased significantly during the early
1970s.

One of the major reasons for this was the fact that
Nixon was successful in his efforts to open diplomatic relations with China.  By doing
this, Nixon put more pressure on the Soviet Union to relax its attitude towards the US. 
The Soviets had to do this for fear of a US-Chinese alliance that would have endangered
Soviet security.

A second reason for this comes not from
Nixon but from the Soviet Union.  The Soviet leaders during this time were not notable
for their hard line attitudes.  This made it much more likely that the policy of detente
would succeed.