How can I get 3 div boxes per line so that only 1 div per line comes out per line?

<div class=thumbnail>
<div class=thumb_wrapper>
<s_article_related_rep_thumbnail>
<div class='related_thumb gen_thumb' 
style='background-image:url("//i1.daumcdn.net/thumb/R0x200/?fname=[##_article_related_rep_thumbnail_link_##]")'>
<div class=gen_black></div>
</div>
</s_article_related_rep_thumbnail>
</div>

.thumbnail{margin:10px;padding:0;border:0}
.thumbnail .caption{padding:10px 0;height:160px}
blockquote{padding:10px 20px;margin:15px;font-size:inherit;border-left:5px
 solid #206776;font-style:italic}.col-lg-1,.col-lg-10,.col-lg-11,.col-lg-12,
.col-lg-2,.col-lg-3,.col-lg-4,.col-lg-5,.col-lg-6,.col-lg-7,.col-lg-8,.col-lg-9,
.col-md-1,.col-md-10,.col-md-11,.col-md-12,.col-md-2,.col-md-3,.col-md-4,
.col-md-5,.col-md-6,.col-md-7,.col-md-8,.col-md-9,.col-sm-1,.col-sm-10,
.col-sm-11,.col-sm-12,.col-sm-2,.col-sm-3,.col-sm-4,.col-sm-5,.col-sm-6,
.col-sm-7,.col-sm-8,.col-sm-9,.col-xs-1,.col-xs-10,.col-xs-11,.col-xs-12,.col-xs-2,
.col-xs-3,.col-xs-4,.col-xs-5,.col-xs-6,.col-xs-7,.col-xs-8,.col-xs-9{padding:0}
.container-wrapper{width:auto!important;max-width:1170px}
#wrapper{padding:2vh 8vw}.txt1{color:#Fa0}.txt2{color:#206776}
.shorthr{width:80px;margin-top:40px}.bottombox{margin-top:24.5px;
padding-top:25px;padding-bottom:25px;background-color:#F8F8F8}
.txt_category{font-size:13px}.txt_date{color:#999;font-size:12px}.txt_title{margin-top:20px;
margin-bottom:40px;font-size:25px}.txt_subtitle{font-size:20px}