As a detective would I have to go through different stages in law enforcement?

Normally an officer works patrol for their probation period, or in a jail or court setting after the academy. To be a detective you have to have police experience, which comes from working patrol where you learn the job, laws, and how to talk with people. Once an officer decides to become a detective there is normally a testing process. Depending on the department there could be a condition that you have to work patrol for x amount of time. The unwritten rule is that a cop as to earn his/her bones in patrol before moving into a speciality assignment. So, to answer your question yes you have to work in patrol first.

Please consider looking up this information below that I have provided at: http://www.payscale.com/research/US/Job=Detective/Salary. This is a great start up tool for information regarding your educational goals and career inspiration(s). I hope that this helps you and good luck!

Job Description for Detective

Typically, detectives are employed by companies to assist in loss and theft prevention. Examples of prospective employers for detectives include insurance companies, which use detectives when determining settlement shares; organizations that require background checks and security clearances, which use detectives as a part of the hiring process; and retail companies, where they may assist with loss prevention.

The essence of what a detective does is to gather data as evidence that will be used to support a conclusion, proposal, or action to be taken by the employer. A detective employed as part of loss prevention in a retail setting may work undercover, walking around their employer's store and looking for suspicious activity; they may also make recommendations to improve security and suggest ways to eliminate temptation. As an investigator for insurance companies, the detective may gather evidence, as well as conduct limited surveillance and perform interviews; the detective then typically presents the data he or she has gathered to assist the company on how to proceed in a claims settlement. When a detective performs background checks for employers, typically they conduct interviews and verification of prior employment and education through records checks.

To work as a detective, a high school diploma or equivalent is generally required; an associate's or bachelor's degree in criminology or a related field may be required or preferred as well. Prior experience is generally needed as well. Detectives must also be excellent communicators to effectively conduct interviews and create reports as required to summarize gathered evidence.
Detective Tasks

Interview sources.
Respond to incidents and complaints, document interactions, and collect evidence.
File reports, documents, and other paperwork.
Collect, store, protect, and analyze physical evidence from crime scenes to aid investigation.
Work closely with team members and other departments.

In nearly every jurisdiction, a detective begins his/her career as a street cop. That is, in order to have the ability and insight to function as a detective, an officer needs exposure and experience on the streets or jail with civilians, victims and suspects. To solve or understand the complexity of cases, an officer develops over time with more understanding and insight. It is best to approach law enforcement with an open mind, open eyes and compassion. You probably do not want a surgeon fresh out of medical school. Experience makes for a better operation!