Benefit Plans Disclosure of Share-based Compensation Arrangements by Share-based Payment Award (Details)
12 Months Ended
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
$ / shares
shares
Dec. 31, 2014
shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Exercised (101,303) (125,000) (369,275)
First Financial Northwest, Inc. 2008 Equity Incentive Plan | Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Outstanding at beginning balance 884,260    
Granted 0    
Exercised (260,440)    
Outstanding at ending balance 603,820 884,260  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]      
Outstanding beginning balance, Weighted Average Exercise Price | $ / shares $ 10.11    
Granted | $ / shares 0.00    
Exercised | $ / shares 9.78    
Outstanding ending balance, Weighted Average Exercise Price | $ / shares $ 10.19 $ 10.11  
Share-based Compensations Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Remaining Contractual Term [Roll Forward]      
Outstanding ending balance, Weighted Average Remaining Contractual Term 4 years 10 months 1 day    
Share Based Compensation, Stock Option Plan, Additional Disclosures [Abstract]      
Outstanding beginning balance, Agregate Intrinsic Value | $    
Exercised | $    
Outstanding ending balance, Agregate Intrinsic Value | $ $ 5,766,947  
Expected to Vest, Shares 598,750    
Expected to Vest, Weighted Average Exercise Price | $ / shares $ 10.18    
Expected to Vest, Weighted Average Remaining Contracutal Term in Years 4 years 9 months 25 days    
Expected to Vest, Aggregate Intrinsic Value | $ $ 5,723,540    
Exercisable ending balance, Shares 434,820    
Exercisable ending balance, Weighted Average Exercise Price 9.80    
Exercisable ending balance, Weighted Average Remaining Contracutal Term in Years 3 years 9 months 18 days    
Exercisable ending balance, Aggregate Intrinsic Value | $ $ 4,320,027    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period 20,000    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price | $ / shares $ 12.05    
First Financial Northwest, Inc. 2008 Equity Incentive Plan | Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Nonvested beginning balance, Shares 47,800    
Granted, Shares 14,052    
Vested, Shares (35,452)    
Nonvested ending balance, Shares 26,400 47,800  
Expected to vest assuming a 3% forfeiture rate over the vesting term, Shares 25,608    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Nonvested beginning balance, Weighted-Average Grant Date Fair Value | $ / shares $ 8.95    
Granted, Weighted-Average Grant Date Fair Value | $ / shares 12.81    
Vested, Weighted-Average Grant Date Fair Value | $ / shares 10.34    
Nonvested ending balance, Weighted-Average Grant Date Fair Value | $ / shares $ 9.13 $ 8.95