Note 6: Loan Servicing

Mortgage loans serviced for others are not included in the accompanying consolidated balance sheets and represent agency eligible multi‑family loans. The risks inherent in mortgage servicing assets relate primarily to changes in prepayments that result from shifts in mortgage interest rates. Call protection is in place to deter from prepayments on a 10‑year sliding scale. The unpaid principal balances of mortgage and other loans serviced for others were $5.0 billion and $4.0 billion at December 31, 2017 and 2016, respectively. Mortgage loans sub‑serviced for others are not included in the accompanying balance sheets. The unpaid principal balances of loans sub‑serviced for others were $2.0 billion and $1.4 billion at December 31, 2017 and 2016, respectively.

The following summarizes the activity in mortgage servicing rights measured using the fair value method for the years ended December 31, 2017, 2016, and 2015:


	For the Year Ended
	December 31,
	2017		2016		2015
		(In thousands)
Balance, beginning of period	$	53,670	$	55,553	$	52,913
Additions
Purchased servicing		1,209		1,357		1,135
Originated servicing		9,784		4,388		6,866
Acquisition of RICHMAC		3,970		—		—
Subtractions
Paydowns		(5,504)		(4,230)		(5,177)
Changes in fair value due to changes in valuation inputs or assumptions used in the valuation model		2,950		(3,398)		(184)
Balance, end of period	$	66,079	$	53,670	$	55,553

Contractually specified servicing fees for retained, purchased and sub‑serviced loans were $8.8 million, $7.5 million, and $6.2 million for the years ended December 31, 2017, 2016 and 2015, respectively.

In connection with certain loan servicing and sub‑servicing agreements, the Company is to reconcile the payments received monthly on these loans, for principal and interest, taxes, insurance, and reserves for replacements. The funds are required to be maintained in separate trust accounts and not commingled with the Company’s general operating funds. At December 31, 2017 and 2016, P/RMIC held restricted escrow funds for these loans, amounting to $502.7 million and $378.5 million, respectively.