The Company accounts for loans held for sale under the fair value option with changes in fair value recognized in current period earnings. At the date of funding of the loan, the funded amount of the loan, the relative derivative asset or liability of the associated interest rate lock commitment, less direct costs, becomes the initial recorded investment in the loan held for sale. Such amount approximates the fair value of the loan. Net gains from changes in estimated fair value of mortgage loans held for sale were $2,354 and $4 for the three-month periods ending March 31, 2020 and 2019, respectively. The total unpaid principal balance of loans held for sale was $185,962 and $141,627 at March 31, 2020 and December 31, 2019, respectively. No loans held for sale at March 31, 2020 or at December 31, 2019 were past due or on nonaccrual.

The table below summarizes the activity in mortgage loans held for sale during the three-month period ending March 31, 2020 and 2019.

	Three-month periods ended
	March 31, 2020	March 31, 2019
Beginning balance	$142,801	$40,399
Loans originated	423,622	134,752
Proceeds from sales	(391,242)	(129,657)
Net change in fair value	2,354	4
Net realized gain on sales	10,781	3,976
Ending balance	$188,316	$49,474

As loans are closed, they are typically sold at prices specified in the forward contracts. Gains or losses may arise if the yields of the loans delivered vary from those specified in the forward contracts. Derivative mortgage loan commitments, or interest rate locks, are also utilized and relate to the origination of a mortgage that will be held for sale upon funding. The Company uses these derivative financial instruments on its loans held for sale to manage interest rate risk and not for speculative purposes. The table below summarizes the main components of Mortgage Banking Revenue during the three-month period ending March 31, 2020 and 2019. The Mortgage Banking Revenue amounts are reported in the Company’s Condensed Consolidated Statements of Income and Comprehensive Income.

	Three-month periods ended
	March 31, 2020	March 31, 2019
Servicing fees and commissions	$83	$93
Gain on sale of loans held for sale	10,781	3,976
Unrealized gain on loans held for sale	2,354	4
(Loss) gain on mortgage derivatives	(1,147)	557
Loss on mortgage hedge	(1,098)	(404)
Loss on mortgage servicing assets	—	(33)
Mortgage banking revenue	$10,973	$4,193

The table below summarizes the notional amounts for interest rate lock commitments, best efforts forward trades and MBS forward trades pertaining to loans held for sale at March 31, 2020 and 2019.

	Notional at
	March 31, 2020	March 31, 2019
Interest rate lock commitments	$389,387	$85,802
Best efforts forward trades	152,788	92,115
MBS forward trades	345,500	57,000
Total derivative instruments	$887,675	$234,917

Mortgage banking derivatives used in the ordinary course of business consist of forward sales contracts and interest rate lock commitments on residential mortgage loans. Forward sales contracts represent future commitments to deliver loans at a specified price and by a specified date and are used to manage interest rate risk on loan commitments and mortgage loans held for sale. Rate lock commitments represent commitments to fund loans at a specific rate and by a specified expiration date. These derivatives involve underlying items, such as interest rates, and are designed to mitigate risk. Notional amounts are amounts on which calculations and payments are based, but which do not represent credit exposure, as credit exposure is limited to the amounts required to be received or paid.