Document and Entity Information	6 Months Ended
	Jun. 30, 2020 shares
Cover [Abstract]
Entity Registrant Name	Waterstone Financial, Inc.
Entity Central Index Key	0001569994
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding	25,906,848
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Document Quarterly Report	true
Document Transition Report	false
Entity Address, State or Province	WI
Entity Incorporation, State or Country Code	MD
Entity File Number	001-36271
Entity Tax Identification Number	90-1026709
Entity Address, Address Line One	11200 W. Plank Court
Entity Address, City or Town	Wauwatosa
Entity Address, Postal Zip Code	53226
City Area Code	414
Local Phone Number	761-1000
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	WSBF
Security Exchange Name	NASDAQ