Benefit Plans Fair Value Assumptions and Methodology (Details) - First Financial Northwest, Inc. 2008 Equity Incentive Plan - Stock Options - $ / shares |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Fair Value, Option, Methodology and Assumptions | Black-Scholes model | ||
| Annual dividend yield | 1.77% | 1.86% | |
| Expected volatility | 35.30% | 37.27% | |
| Risk-free interest rate | 2.23% | 2.44% | |
| Expected term | 10 years | 10 years | |
| Weighted-average grant date fair value per option granted | $ 4.74 | $ 4.13 | |