My question involves labor and employment law for the state of: California

My current company had me sign an agreement prior to joining the company that I would agree to work for a period of one year and that if I terminated my employment before one year I may be required to pay back a pro-rated rate of some of the cost of the security clearance background investigation that was conducted for my employment. I am leaving the company prior to one year because a really great opportunity arose that I just could not pass up. I fully understand my obligation to pay back and have every intention to. My question is, if I ask for an itemized list showing me exactly how they calculated and reached the cost amount that I'm required to pay back, will they be required to show this to me? Or am I supposed to blindly accept whatever amount they say I must pay them and pay that amount without really knowing how they got to that number? The contract did not state anything about this simply that "If I separate prior to one year I MAY be required to pay pay back pro-rated amount". If they tell me I must pay back roughly $2,000 I would like to know exactly what I am paying for to be sure they aren't over charging me. Is that some time of legal requirement if I ask for it?

Thanks!