8. OTHER INTANGIBLE ASSETS

Other intangible assets include a core deposit premium and mortgage servicing rights. The following table presents changes in other intangible assets for the three months ended March 31, 2014:

	Core			Mortgage
	Deposit			Servicing
	Premium			Rights			Total
	(Dollars in thousands)

Balance, beginning of period	$	12,704		$	20,079		$	32,783
Additions	—			408			408
Amortization	(669		)	(571		)	(1,240		)
Balance, end of period	$	12,035		$	19,916		$	31,951

Income generated as the result of new mortgage servicing rights is reported as gains on sales of loans and totaled $0.4 million and $0.9 million for the three months ended March 31, 2014 and 2013, respectively. Amortization of mortgage servicing rights was $0.6 million and $1.6 million for the three months ended March 31, 2014 and 2013, respectively.

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 March 31,
	2014			2013
	(Dollars in thousands)

Fair market value, beginning of period	$	21,399		$	22,356
Fair market value, end of period	20,832			21,595
Weighted average discount rate	8.0		%	8.0		%
Weighted average prepayment speed assumption	14.1			14.1

The gross carrying value and accumulated amortization related to our intangible assets are presented below:

	March 31, 2014							December 31, 2013
	Gross							Gross
	Carrying		Accumulated					Carrying		Accumulated
	Value		Amortization			Net		Value		Amortization			Net
	(Dollars in thousands)

Core deposit premium	$	44,642	$	(32,607	)	$	12,035	$	44,642	$	(31,938	)	$	12,704
Mortgage servicing rights	54,849		(34,933		)	19,916		54,441		(34,362		)	20,079
	$	99,491	$	(67,540	)	$	31,951	$	99,083	$	(66,300	)	$	32,783

Based on the core deposit premium and mortgage servicing rights held as of March 31, 2014, estimated amortization expense for the remainder of fiscal 2014, the next five succeeding fiscal years and all years thereafter are as follows:

	Estimated Amortization Expense
			Mortgage
	Core Deposit		Servicing
	Premium		Rights		Total
	(Dollars in thousands)

2014 (remainder)	$	2,006	$	1,720	$	3,726
2015	2,674		1,860		4,534
2016	2,674		1,445		4,119
2017	2,674		1,146		3,820
2018	2,007		887		2,894
2019	—		678		678
Thereafter	—		12,180		12,180
	$	12,035	$	19,916	$	31,951

We perform an impairment assessment of our other intangible assets whenever events or changes in circumstance indicate that the carrying value of those assets may not be recoverable. Our impairment assessments involve, among other valuation methods, the estimation of future cash flows and other methods of determining fair value. Estimating future cash flows and determining fair values is subject to judgment and often involves the use of significant estimates and assumptions. The variability of the factors we use to perform our impairment tests depend on a number of conditions, including the uncertainty about future events and cash flows. All such factors are interdependent and, therefore, do not change in isolation. Accordingly, our accounting estimates may materially change from period to period due to changing market factors.