http://news.bbc.co.uk/2/hi/middle_east/8374402.stm
Israel is one of the few regimes in the world that have a hostage taking policy - including holding parliamentarians (and women and children) as hostage. Note that 'administrative detention' is a euphemism for kidnapping and keeping hostage - the people are not held on any charges and haven't committed any crimes (otherwise they would be charged).
Israel holds about 10,000 Palestinian prisoners in jail on security grounds - a major bone of contention with the Palestinians.
Earlier this month, several Hamas MPs were freed without charge after the 40-month period of their administrative detention expired. Fifteen Hamas MPs and two from Fatah remain in detention.
Cheers,
Shafique