8. CORE DEPOSIT PREMIUM AND MORTGAGE SERVICING RIGHTS

The following table presents changes in core deposit premium and mortgage servicing rights for the six months ended June 30, 2018:



(dollars in thousands)	Core Deposit Premium			Mortgage Servicing Rights			Total
Balance, beginning of period	$	2,006		$	15,843		$	17,849
Additions	—			807			807
Amortization	(1,337		)	(894		)	(2,231		)
Balance, end of period	$	669		$	15,756		$	16,425

Income generated as the result of new mortgage servicing rights is reported as gains on sales of loans and totaled $0.4 million and $0.8 million for the three and six months ended June 30, 2018, respectively, compared to $0.6 million and $1.2 million for the three and six months ended June 30, 2017, respectively.

Amortization of mortgage servicing rights was $0.4 million and $0.9 million, respectively, for the three and six months ended June 30, 2018, compared to $0.5 million and $1.1 million for the three and six months ended June 30, 2017, respectively.

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



	Six Months Ended			Six Months Ended
(dollars in thousands)	June 30, 2018			June 30, 2017
Fair market value, beginning of period	$	17,161		$	18,087
Fair market value, end of period	18,560			17,024
Weighted average discount rate	9.5		%	9.5		%
Forecasted constant prepayment rate assumption	13.9			16.1

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



	June 30, 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	$	(43,973	)	$	669	$	44,642	$	(42,636	)	$	2,006
Mortgage servicing rights	65,208		(49,452		)	15,756		64,401		(48,558		)	15,843
Total	$	109,850	$	(93,425	)	$	16,425	$	109,043	$	(91,194	)	$	17,849

Based on the core deposit premium and mortgage servicing rights held as of June 30, 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)	$	669	$	770	$	1,439
2019	—		1,323		1,323
2020	—		1,113		1,113
2021	—		934		934
2022	—		793		793
2023	—		698		698
Thereafter	—		10,125		10,125
	$	669	$	15,756	$	16,425

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.