Nested form accepts_nested_attributes_for giving dynamic Array - Rails4 - ruby-on-rails

Question

I am working on Rails4 with Nested form, accepts_nested_attributes_for i can able to generate the nested form but its giving dynamic array the the form when i inspect the form.
<input type="text" name="event_venue[event_contact_details_attributes][1403763304978][name]" id="event_venue_event_contact_details_attributes_1403763304978_name" class="form-control">
But it should be,
<input type="text" name="event_venue[event_contact_details_attributes][1][name]" id="event_venue_event_contact_details_attributes_1_name" class="form-control">
<div class="formWrapper">
<div class="col-md-6">
<div class="form-group">
<label for="exampleInputEmail1">Name</label>
<input type="text" name="event_venue[event_contact_details_attributes][1403764358820][name]" id="event_venue_event_contact_details_attributes_1403764358820_name" class="form-control">
</div>
<div class="form-group">
<label for="exampleInputEmail1">Phone</label>
<input type="text" name="event_venue[event_contact_details_attributes][1403764358820][telephone]" id="event_venue_event_contact_details_attributes_1403764358820_telephone" class="form-control">
</div>
<div class="form-group">
<label for="exampleInputEmail1">Email</label>
<input type="text" name="event_venue[event_contact_details_attributes][1403764358820][email]" id="event_venue_event_contact_details_attributes_1403764358820_email" class="form-control">
</div>
<div class="clearfix"></div>
<input type="hidden" value="false" name="event_venue[event_contact_details_attributes][1403764358820][_destroy]" id="event_venue_event_contact_details_attributes_1403764358820__destroy"><a onclick="remove_fields(this); return false;" href="#">remove</a>
</div>
</div>
Can you help me out where i am missing the things...!!!
In first nested form set it's coming right,
<div class="formWrapper">
<div class="col-md-6">
<div class="form-group">
<label for="exampleInputEmail1">Name</label>
<input type="text" value="AS" name="event_venue[event_contact_details_attributes][0][name]" id="event_venue_event_contact_details_attributes_0_name" class="form-control">
</div>
<div class="form-group">
<label for="exampleInputEmail1">Phone</label>
<input type="text" value="AS" name="event_venue[event_contact_details_attributes][0][telephone]" id="event_venue_event_contact_details_attributes_0_telephone" class="form-control">
</div>
<div class="form-group">
<label for="exampleInputEmail1">Email</label>
<input type="text" value="AS" name="event_venue[event_contact_details_attributes][0][email]" id="event_venue_event_contact_details_attributes_0_email" class="form-control">
</div>
<div class="clearfix"></div>
<input type="hidden" value="false" name="event_venue[event_contact_details_attributes][0][_destroy]" id="event_venue_event_contact_details_attributes_0__destroy"><a onclick="remove_fields(this); return false;" href="#">remove</a>
</div>
</div>
Event Venue Model,
has_many :event_contact_details, :dependent => :destroy
accepts_nested_attributes_for :event_contact_details, allow_destroy: true
Controller,
def new
#event_venue = EventVenue.new
#event_venue.event_contact_details.build
end
form,
<%= f.fields_for :event_contact_details do |builder| %>
<%= render :partial => 'event_venues/event_contact_detail_fields',
:locals => { :f => builder } %>
<% end %>
<p><%= link_to_add_fields "Add More", f, :event_contact_details %></p>