Loans Receivable - Troubled Debt Restructuring Schedule of Modified Loans (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($) contract	Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($) contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification, number of contracts | contract	1	2	4,000
Financing receivable, modifications, pre-modification recorded investment	$ 244	$ 180	$ 562
Financing receivable, modifications, post-modification, number of contracts | contract	1	2	4,000
Financing receivable, modifications, post-modification recorded investment	$ 236	$ 179	$ 544
One-to-four family | Real Estate | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification, number of contracts | contract	1	2	3,000
Financing receivable, modifications, pre-modification recorded investment	$ 244	$ 180	$ 428
Financing receivable, modifications, post-modification, number of contracts | contract	1	2	3,000
Financing receivable, modifications, post-modification recorded investment	$ 236	$ 179	$ 415
Commercial real estate | Commercial business loans | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification, number of contracts | contract			1,000
Financing receivable, modifications, pre-modification recorded investment			$ 134
Financing receivable, modifications, post-modification, number of contracts | contract			1,000
Financing receivable, modifications, post-modification recorded investment			$ 129
Rate Modification
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment	0	0	95
Financing receivable, modifications, post-modification recorded investment	0	0	92
Rate Modification | One-to-four family | Real Estate | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment	0	0	95
Financing receivable, modifications, post-modification recorded investment	0	0	92
Rate Modification | Commercial real estate | Commercial business loans | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment			0
Financing receivable, modifications, post-modification recorded investment			0
Term Modification
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment	0	0	89
Financing receivable, modifications, post-modification recorded investment	0	0	87
Term Modification | One-to-four family | Real Estate | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment	0	0	89
Financing receivable, modifications, post-modification recorded investment	0	0	87
Term Modification | Commercial real estate | Commercial business loans | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment			0
Financing receivable, modifications, post-modification recorded investment			0
Combination Modification
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment	244	180	378
Financing receivable, modifications, post-modification recorded investment	236	179	365
Combination Modification | One-to-four family | Real Estate | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment	244	180	244
Financing receivable, modifications, post-modification recorded investment	$ 236	$ 179	236
Combination Modification | Commercial real estate | Commercial business loans | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, pre-modification recorded investment			134
Financing receivable, modifications, post-modification recorded investment			$ 129