The Company, through its subsidiary bank, borrows funds in the form of federal funds purchased and Federal Home Loan Bank advances.

Federal fund lines of credit are extended to the Bank by nonaffiliated banks with which a correspondent banking relationship exists. The line of credit amount is determined by the creditworthiness of the Bank and, in particular, its regulatory capital ratios, which are discussed in Note 15. Federal funds purchased generally mature each business day. The following table summarizes information related to federal funds purchased for the years ended December 31, 2020 and 2019:

	December 31,
	2020			2019
	(dollars in thousands)
Balance at year-end		—			—
Average balance during the year		1			1,074
Average interest rate during the year		0.61	%		2.91	%
Maximum month-end balance during the year	$	—		$	10,780
Gross lines of credit at year-end		28,000			28,000
Unused lines of credit at year-end		28,000			28,000

As of December 31, 2020, Company had remaining credit availability in the amount of $225.2 million with the Federal Home Loan Bank of Atlanta. This line may be utilized for short and/or long-term borrowing. Advances on the line are secured by all of the Company’s eligible first lien residential real estate loans on one-to-four-unit, single-family dwellings; multi-family dwellings; home equity lines of credit; and commercial real estate loans. The amount of the available credit is limited to a percentage of the estimated market value of the loans as determined periodically by the FHLB of Atlanta. The amount of the available credit is also limited to 20% of total Bank assets.

The Company had no borrowings with the FHLB at December 31, 2020 or December 31, 2019. The Company had a $50.0 million irrevocable letter of credit at December 31, 2020 with the FHLB to secure public deposits.