FIRST FINANCIAL NORTHWEST, INC. AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss), net of tax	Unearned ESOP Shares
Balances at beginning of period (in shares) at Dec. 31, 2017	10,748,437
Balances at beginning of period at Dec. 31, 2017	$ 142,634	$ 107	$ 94,173	$ 54,642	$ (928)	$ (5,360)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,944			9,944
Other comprehensive income	$ (1,217)				(1,217)
Exercise of stock options (in shares)	137,940
Exercise of stock options	$ 1,365	1	1,364
Issuance of common stock - restricted stock awards, net	30,179
Issuance of common stock - restricted stock awards, net	$ 1	1	0
Compensation related to stock options and restricted stock awards	409		409
Allocation of ESOP shares	962		398			564
Cash dividend declared and paid	(1,544)			1,544
Balances at end of period at Jun. 30, 2018	$ 152,554	109	96,344	63,042	(2,145)	(4,796)
Balances at end of period (in shares) at Jun. 30, 2018	10,916,556
Balances at beginning of period (in shares) at Mar. 31, 2018	10,779,424
Balances at beginning of period at Mar. 31, 2018	$ 148,755	108	94,527	60,767	(1,568)	(5,079)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,102			3,102
Other comprehensive income	$ (577)				(577)
Exercise of stock options (in shares)	127,940
Exercise of stock options	$ 1,267	1	1,266
Issuance of common stock - restricted stock awards, net	9,192
Issuance of common stock - restricted stock awards, net	$ 0	0	0
Compensation related to stock options and restricted stock awards	326		326
Allocation of ESOP shares	508		225			283
Cash dividend declared and paid	(827)			827
Balances at end of period at Jun. 30, 2018	$ 152,554	109	96,344	63,042	(2,145)	(4,796)
Balances at end of period (in shares) at Jun. 30, 2018	10,916,556
Balances at beginning of period (in shares) at Dec. 31, 2018	10,710,656
Balances at beginning of period at Dec. 31, 2018	$ 153,738	107	93,773	66,343	(2,253)	(4,232)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,249			5,249
Other comprehensive income	$ 944				944
Issuance of common stock - restricted stock awards, net	16,698
Issuance of common stock - restricted stock awards, net	$ (93)	0	(93)
Compensation related to stock options and restricted stock awards	231		231
Allocation of ESOP shares	$ 887		323			564
Repurchase and retirement of common stock (in shares)	(346,100)
Repurchase and retirement of common stock	$ 5,512	3	5,509	0	0	0
Canceled common stock - restricted stock awards (in shares)	(5,929)
Cash dividend declared and paid	$ (1,703)			(1,703)
Balances at end of period at Jun. 30, 2019	$ 153,828	104	88,725	69,976	(1,309)	(3,668)
Balances at end of period (in shares) at Jun. 30, 2019	10,375,325
Balances at beginning of period (in shares) at Mar. 31, 2019	10,457,625
Balances at beginning of period at Mar. 31, 2019	$ 151,684	104	89,800	67,568	(1,838)	(3,950)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,304			3,304
Other comprehensive income	529				529
Compensation related to stock options and restricted stock awards	107		107
Allocation of ESOP shares	$ 442		160			282
Repurchase and retirement of common stock (in shares)	(82,300)
Repurchase and retirement of common stock	$ 1,342	0	1,342	0	0	0
Cash dividend declared and paid	(896)			(896)
Balances at end of period at Jun. 30, 2019	$ 153,828	$ 104	$ 88,725	$ 69,976	$ (1,309)	$ (3,668)
Balances at end of period (in shares) at Jun. 30, 2019	10,375,325