8. CORE DEPOSIT PREMIUM AND MORTGAGE SERVICING RIGHTS

The following table presents changes in core deposit premium and mortgage servicing rights for the three months ended March 31, 2018:



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

Income generated as the result of new mortgage servicing rights is reported as gains on sales of loans and totaled $0.4 million for the three months ended March 31, 2018, compared to $0.6 million for the three months ended March 31, 2017.

Amortization of mortgage servicing rights was $0.5 million for the three months ended March 31, 2018, compared to $0.5 million for the three months ended March 31, 2017.

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



(dollars in thousands)	March 31, 2018			March 31, 2017
Fair market value, beginning of period	$	17,161		$	18,087
Fair market value, end of period	18,463			17,627
Weighted average discount rate	9.5		%	9.5		%
Forecasted constant prepayment rate assumption	14.2			15.0

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



	March 31, 2018							December 31, 2017
(dollars in thousands)	Gross Carrying Value		Accumulated Amortization			Net Carrying Value		Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Core deposit premium	$	44,642	$	(43,305	)	$	1,337	$	44,642	$	(42,636	)	$	2,006
Mortgage servicing rights	64,836		(49,015		)	15,821		64,401		(48,558		)	15,843
Total	$	109,478	$	(92,320	)	$	17,158	$	109,043	$	(91,194	)	$	17,849

Based on the core deposit premium and mortgage servicing rights held as of March 31, 2018, estimated amortization expense for the remainder of fiscal year 2018, the next five succeeding fiscal years and all years thereafter are as follows:



	Estimated Amortization Expense
(dollars in thousands)	Core Deposit Premium		Mortgage Servicing Rights		Total
2018 (remainder)	$	1,337	$	1,076	$	2,413
2019	—		1,211		1,211
2020	—		1,017		1,017
2021	—		867		867
2022	—		733		733
2023	—		663		663
Thereafter	—		10,254		10,254
	$	1,337	$	15,821	$	17,158

We perform an impairment assessment of our core deposit premium and mortgage servicing rights whenever events or changes in circumstance indicate that the carrying value of those assets may not be recoverable.