7. CORE DEPOSIT PREMIUM AND MORTGAGE SERVICING RIGHTS

The following table presents changes in core deposit premium and mortgage servicing rights for the periods presented:



(dollars in thousands)	Core Deposit Premium			Mortgage Servicing Rights			Total
Balance, January 1, 2018	$	2,006		$	15,843		$	17,849
Additions	—			435			435
Amortization	(669		)	(457		)	(1,126		)
Balance, March 31, 2018	$	1,337		$	15,821		$	17,158

Balance, January 1, 2019	$	—		$	15,596		$	15,596
Additions	—			222			222
Amortization	—			(471		)	(471		)
Balance, March 31, 2019	$	—		$	15,347		$	15,347

Income generated as the result of new mortgage servicing rights is reported as gains on sales of loans and totaled $0.2 million for the three months ended March 31, 2019 compared to $0.4 million for the three months ended March 31, 2018.

Amortization of mortgage servicing rights was $0.5 million for the three months ended March 31, 2019, compared to $0.5 million for the three months ended March 31, 2018.

The following table presents the fair market value and key assumptions used in determining the fair market value of our mortgage servicing rights:



	Three Months Ended			Three Months Ended
(dollars in thousands)	March 31, 2019			March 31, 2018
Fair market value, beginning of period	$	17,696		$	17,161
Fair market value, end of period	16,541			18,463
Weighted average discount rate	9.5		%	9.5		%
Forecasted constant prepayment rate assumption ⁽¹⁾	16.2			14.2

⁽¹⁾ Represents annualized loan prepayment rate assumption.

The gross carrying value and accumulated amortization related to our core deposit premium and mortgage servicing rights are presented below:



	March 31, 2019							December 31, 2018
(dollars in thousands)	Gross Carrying Value		Accumulated Amortization			Net Carrying Value		Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Core deposit premium	$	44,642	$	(44,642	)	$	—	$	44,642	$	(44,642	)	$	—
Mortgage servicing rights	66,235		(50,888		)	15,347		66,013		(50,417		)	15,596
Total	$	110,877	$	(95,530	)	$	15,347	$	110,655	$	(95,059	)	$	15,596

Based on the mortgage servicing rights held as of March 31, 2019, estimated amortization expense for the remainder of fiscal year 2019, the next five succeeding fiscal years and all years thereafter are as follows:



(dollars in thousands)
2019 (remainder)	$	1,263
2020	1,382
2021	1,130
2022	945
2023	786
2024	704
Thereafter	9,137
Total	$	15,347

We perform an impairment assessment of our mortgage servicing rights whenever events or changes in circumstance indicate that the carrying value of the asset may not be recoverable.