Benefit Plans Disclosure of Share-based Compensation Arrangements by Share-based Payment Award (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	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 January 1, 2012, Shares	1,448,524	1,373,524	1,383,524
Granted, Shares	110,000	100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(314,989)
Forfeited or expired, Shares	(40,000)	(25,000)	(10,000)
Outstanding at December 31, 2012, Shares	1,203,535	1,448,524	1,373,524
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding at January 1, 2012, Weighted Average Exercise Price	$ 9.41	$ 9.52	$ 9.52
Granted, Weighted Average Exercise Price	$ 10.79	$ 8.08
Exercised, Weighted Average Exercise Price	$ 9.60
Forfeited or expired, Weighted Average Exercise Price	$ 9.42	$ 9.78	$ 9.78
Outstanding at December 31, 2012, Weighted Average Exercise Price	$ 9.49	$ 9.41	$ 9.52
Share-based Compensations Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Remaining Contractual Term [Roll Forward]
Outstanding at January 1, 2012, Weighted Average Remaining Contractual Term	5 years 4 months 28 days
Outstanding at December 31, 2012, Weighted Average Remaining Contractual Term	5 years 4 months 28 days
Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding at December 31, 2012, Weighted Average Grant Date Fair Value	$ 2.11
Agregate Intrinsic Value	$ 1,103,186,000
Share Based Compensation, Stock Option Plan, Additional Disclosures [Abstract]
Expected to Vest, Shares	1,197,235
Expected to Vest, Weighted Average Exercise Price	$ 9.49
Expected to Vest, Weighted Average Remaining Contracutal Term in Years	5 years 4 months 21 days
Expected to Vest, Aggregate Intrinsic Value	1,093,874,000
Exercisable at December 31, 2012, Shares	993,535
Exercisable at December 31, 2012, Weighted Average Exercise Price	9.57
Exercisable at December 31, 2012, Weighted Average Remaining Contracutal Term in Years	4 years 7 months 24 days
Exercisable at December 31, 2012, Aggregate Intrinsic Value	792,786,000
First Financial Northwest, Inc. 2008 Equity Incentive Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 1,500,000	$ 1,400,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested at January 1, 2012, Shares	244,847	310,494	456,140
Granted, Shares	25,000	82,000
Vested, Shares	(156,047)	(143,647)	(145,646)
Forfeited, Shares	(10,400)	(4,000)
Nonvested at December 31, 2012, Shares	103,400	244,847	310,494
Expected to vest assuming a 3% forfeiture rate over the vesting term, Shares	100,298
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Nonvested at January 1, 2012, Weighted-Average Grant Date Fair Value	$ 8.95	$ 9.66	$ 9.75
Granted, Weighted-Average Grant Date Fair Value	$ 10.88	$ 8.06
Vested, Weighted-Average Grant Date Fair Value	$ 9.72	$ 9.93	$ 9.93
Forfeited, Weighted-Average Grant Date Fair Value	$ 9.12	$ 10.35
Nonvested at December 31, 2012, Weighted-Average Grant Date Fair Value	$ 8.24	$ 8.95	$ 9.66