v3.5.0.2
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2016
Oct. 31, 2016
Document and Entity Information [Abstract]    
Entity Registrant Name NMI HOLDINGS, INC.  
Entity Central Index Key 0001547903  
Document Type 10-Q  
Document Period End Date Sep. 30, 2016  
Amendment Flag false  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q3  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   59,138,663