MORTGAGE SERVICING RIGHTS

Mortgage servicing rights--Mortgage loans serviced for others are not included in the accompanying consolidated balance sheets. The unpaid balances of the one- to four-family residential real estate loans as of December 31, 2019 and December 31, 2018 were $524,715 and $518,476, respectively. These residential mortgage loans are serviced primarily for the Federal Home Loan Mortgage Corporation, Federal Home Loan Bank and the Federal National Mortgage Association.

Custodial escrow balances maintained in connection with the foregoing loan servicing, and included in deposits were $2,868 and $3,182, at December 31, 2019 and December 31, 2018, respectively. Mortgage servicing rights activity for the year ended December 31, 2019 and the three months ended December 31, 2018 were as follows:



	As of and for the twelve months ended			As of and for the three months ended			As of and for the twelve months ended
	December 31, 2019			December 31, 2018			September 30, 2018
Mortgage servicing rights:
Mortgage servicing assets, net; beginning of period	$	4,486		$	1,840		$	1,886
MSR asset acquired	—			2,721			—
Increase in MSR assets resulting from transfers of financial assets	904			100			289
Amortization during the period	(849		)	(175		)	(335		)
	4,541			4,486			1,840
Valuation Allowances:
Balance at beginning of period	—			—			—
Additions	(259		)	—			—
Recoveries	—			—			—
Write-downs	—			—			—
Balance at end of period	(259		)	—			—
Mortgage servicing assets, net; end of period	$	4,282		$	4,486		$	1,840
Fair value of MSR asset; end of period	$	4,309		$	5,214		$	2,669
Residential mortgage loans serviced for others	$	524,715		$	518,476		$	281,289
Net book value of MSR asset to loans serviced for others	0.82		%	0.87		%	0.65		%

At December 31, 2019, the estimated future aggregate amortization expense for the MSRs is as follows. The estimated amortization expense is based on existing mortgage servicing asset balances. The timing of amortization expense actually recognized in future periods may differ significantly based on actual prepayment speeds, mortgage interest rates and other factors.



	Amortization Expense
2020	$	987
2021	841
2022	696
2023	557
2024	418
After 2024	783
Total	$	4,282