Goodwill. At December 31, 2019 and 2018, the carrying value of goodwill, which is included in other assets, totaled $31.2 million and $412,000, respectively. Goodwill is tested for impairment, based on its fair value, at least annually. As of December 31, 2019 and 2018, no goodwill impairment has been recognized.

Core deposit intangibles. The Company recorded an asset for the core deposit intangible (“CDI”) of $3.6 million related to the Optima merger. Amortization of CDI assets totaled $270,000 for the twelve months ended December 31, 2019. As of December 31, 2019, the carrying value of CDI assets totaled $3.3 million . The weighted-average remaining amortization period for CDI was approximately nine years at December 31, 2019.

Mortgage servicing rights. Periodically, the Company sells certain residential mortgage loans to the secondary market. Generally, these loans are sold without recourse or other credit enhancements.

The Company sells loans and either releases or retains the servicing rights. For loans sold with servicing rights retained, we provide the servicing for the loans on a per-loan fee basis. Mortgage loans sold and servicing rights retained during the years ended December 31, 2019, 2018, and 2017 were $82.9 million, $1.6 million, and $11.9 million, respectively, with net gains recognized in gain on loan sales of $685,000, $36,000, and $182,000, respectively.

An analysis of mortgage servicing rights, which are included in other assets, follows:

	Mortgage Servicing Rights			Valuation Allowance			Total
	(dollars in thousands)
Balance at December 31, 2016	$	842		$	(30	)	$	812
Mortgage servicing rights capitalized		132			—			132
Amortization charged against servicing income		(151	)		—			(151	)
Change in impairment reserve		—			—			—
Balance at December 31, 2017	$	823		$	(30	)	$	793

Mortgage servicing rights capitalized		20			—			20
Amortization charged against servicing income		(147	)		—			(147	)
Change in impairment reserve		(30	)		30			—
Balance at December 31, 2018	$	666		$	—		$	666

Mortgage servicing rights acquired as a result of the merger		334			—			334
Mortgage servicing rights capitalized		618			—			618
Amortization charged against servicing income		(271	)		—			(271	)
Change in impairment reserve		—			(26	)		(26	)
Balance at December 31, 2019	$	1,347		$	(26	)	$	1,321

The fair value of our mortgage servicing rights (“MSR”) portfolio was $1.5 million and $1.0 million as of December 31, 2019 and 2018. The fair value of mortgage servicing rights is estimated based on the present value of expected cash flows, incorporating assumptions for discount rate, prepayment speed, and servicing cost.

The weighted-average amortization period for mortgage servicing rights portfolio was 5.2 years and 7.5 years at December 31, 2019 and December 31, 2018, respectively.

The estimated aggregate future amortization expense for mortgage servicing rights for each of the next five years and thereafter is as follows: