OTHER INTANGIBLE ASSETS

The following table shows the net carrying value of the Corporation's other intangible assets:



	December 31,
	2014		2013
	(In thousands)
Other intangible assets:
Core deposit intangible assets	$	20,863	$	10,001
Mortgage servicing rights (MSRs)	12,217		3,423
Total other intangible assets	$	33,080	$	13,424

Core Deposit Intangible Assets

The following table sets forth the carrying amount, accumulated amortization and amortization expense of core deposit intangible assets that are amortizable and arose from business combinations or other acquisitions:



	December 31,
	2014		2013
	(In thousands)
Gross original amount	$	31,550	$	18,659
Accumulated amortization	10,687		8,658
Carrying amount	$	20,863	$	10,001
Amortization expense for the year ended December 31	$	2,029	$	1,909

In conjunction with the acquisition of Northwestern in 2014, the Corporation recorded $12.9 million in core deposit intangible assets. There were no additions of core deposit intangible assets during 2013.

The estimated future amortization expense on core deposit intangible assets for the years ending after December 31, 2014 is as follows: 2015 - $3.2 million; 2016 - $2.9 million; 2017 - $2.6 million; 2018 - $2.5 million; 2019 - $2.4 million; 2020 and thereafter - $7.3 million.

Mortgage Servicing Rights (MSRs)

The following shows the net carrying value and fair value of MSRs and the total loans that the Corporation is servicing for others:



	December 31,
	2014		2013
	(In thousands)
Net carrying value of MSRs	$	12,217	$	3,423
Fair value of MSRs	$	14,979	$	6,878
Loans serviced for others that have servicing rights capitalized	$	2,093,140	$	886,730

The fair value of MSRs was estimated by calculating the present value of estimated future net servicing cash flows, taking into consideration expected prepayment rates, discount rates, servicing costs and other economic factors that are based on current market conditions. The prepayment rates and the discount rate are the most significant factors affecting valuation of the MSRs. Increases in mortgage loan prepayments reduce estimated future net servicing cash flows because the life of the underlying loan is reduced. Expected loan prepayment rates are validated by a third-party model. At December 31, 2014, the weighted average coupon rate, discount rate and constant prepayment rate (CPR) of the Corporation's $881 million originated servicing portfolio was 4.28%, 8.5% and 13.6%, respectively, while the weighted average coupon rate, discount rate and CPR of the Corporation's $1.21 billion acquired servicing portfolio was 4.08%, 10.1% and 11.65%, respectively. At December 31, 2013, the weighted average coupon rate of the Corporation's originated servicing portfolio was 4.33%, the discount rate was 8.5% and the CPR was 11.3%.

The following shows activity for capitalized MSRs for the last three years:



	Years Ended December 31,
	2014			2013			2012
	(In thousands)
Balance at beginning of year	$	3,423		$	3,478		$	3,593
Acquired in Northwestern acquisition	9,235			—			—
Additions	1,075			1,528			2,285
Amortization	(1,316		)	(1,583		)	(2,400		)
Increase in valuation allowance	(200		)	—			—
Balance at end of year	$	12,217		$	3,423		$	3,478
Valuation allowance at December 31	$	200		$	—		$	—

MSRs are stratified into servicing assets originated by the Corporation and those acquired in acquisitions of other institutions and further stratified into relatively homogeneous pools based on products with similar characteristics. The MSR impairment valuation allowance recorded at December 31, 2014 related to impairment within certain pools attributable to the Corporation's servicing portfolio that was acquired in the Northwestern transaction.