Benefit Plans Disclosure of Share-based Compensation Arrangements by Share-based Payment Award (Details)
12 Months Ended
Dec. 31, 2015
USD ($)
$ / shares
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2013
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Exercised (125,000) (369,275) (314,989)
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 929,260    
Granted 80,000    
Exercised (125,000)    
Outstanding at ending balance 884,260 929,260  
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 $ 9.51    
Granted | $ / shares 12.98    
Exercised | $ / shares 7.48    
Outstanding ending balance, Weighted Average Exercise Price | $ / shares $ 10.11 $ 9.51  
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 11 months 5 days    
Share Based Compensation, Stock Option Plan, Additional Disclosures [Abstract]      
Outstanding beginning balance, Agregate Intrinsic Value | $ $ 0    
Exercised | $ 0    
Outstanding ending balance, Agregate Intrinsic Value | $ $ 3,403,707 $ 0  
Expected to Vest, Shares 876,400    
Expected to Vest, Weighted Average Exercise Price | $ / shares $ 10.10    
Expected to Vest, Weighted Average Remaining Contracutal Term in Years 4 years 10 months 24 days    
Expected to Vest, Aggregate Intrinsic Value | $ $ 3,380,786    
Exercisable ending balance, Shares 622,260    
Exercisable ending balance, Weighted Average Exercise Price 9.72    
Exercisable ending balance, Weighted Average Remaining Contracutal Term in Years 3 years 5 months 16 days    
Exercisable ending balance, Aggregate Intrinsic Value | $ $ 2,639,687    
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 75,600 103,400 244,847
Granted, Shares     25,000
Vested, Shares (27,800) (27,800) (156,047)
Forfeited, Shares     (10,400)
Nonvested ending balance, Shares 47,800 75,600 103,400
Expected to vest assuming a 3% forfeiture rate over the vesting term, Shares 46,366    
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 $ 8.47 $ 8.24 $ 8.95
Granted, Weighted-Average Grant Date Fair Value | $ / shares     10.88
Vested, Weighted-Average Grant Date Fair Value | $ / shares 7.64 7.64 9.72
Forfeited, Weighted-Average Grant Date Fair Value | $ / shares     9.12
Nonvested ending balance, Weighted-Average Grant Date Fair Value | $ / shares $ 8.95 $ 8.47 $ 8.24