Loans Receivable and Allowance for Loan Losses - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Loan	Dec. 31, 2017 USD ($) Loan	Dec. 31, 2016 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Restructured loans | Loan	0	1
Number of troubled debt restructured loans, included in impaired loans | Loan	40	49
Impaired loans	$ 17,225	$ 25,160	$ 26,075
Impairment reserves	618	922	$ 1,373
Troubled Debt Restructured Loans
Accounts Notes And Loans Receivable [Line Items]
Impaired loans	14,104	18,371
Impairment reserves	$ 618	$ 921
Maximum
Accounts Notes And Loans Receivable [Line Items]
Creditworthiness of each customer to the market value of the collateral at the date of the credit extension percentage	75.00%
Minimum
Accounts Notes And Loans Receivable [Line Items]
Strong Pass Loans to new or existing borrowers collateralized percentage	90.00%