(in thousands)	December 31,
	2020			2019
Unsecured revolving lines of credit	$	122,771		$	193,459
3.68% Series B senior notes due in 2021		40,000			40,000
3.84% Series C senior notes due in 2022		60,000			60,000
		222,771			293,459
Unamortized debt issuance cost		(17	)		(28	)
	$	222,754		$	293,431

As of December 31, 2020, the future minimum payments under the unsecured revolving lines of credit, 3.68% Series B senior notes due in 2021 and 3.84% Series C senior notes due in 2022 are as follows:

(in thousands)
Year Ended December 31,
2021	$	40,000
2022		60,000
2023		—
2024		—
2025		122,771
	$	222,771

On March 31, 2020, the Company entered into an amended and restated credit agreement with Bank of America, N.A., as Administrative Agent, Swing Line Lender, L/C Issuer and lender, and other lenders named therein (the “Credit Facility”). The Credit Facility provides for a $420.0 million unsecured revolving credit facility (which may be further increased to $670.0 million by adding one or more tranches of term loans and/or increasing the aggregate revolving commitments), which includes a $25.0 million sublimit for the issuance of standby letters of credit and a $10.0 million sublimit for swingline loans. The proceeds of the Credit Facility are available to be used for general corporate purposes, including permitted acquisitions. The Credit Facility permits the Company’s existing indebtedness to remain, which includes the Company’s $12.0 million Treasury Sweep Note due March 31, 2025, the Company’s existing senior notes issued pursuant to the Note Purchase and Private Shelf Agreement with Prudential Investment Management, Inc., dated as of April 21, 2011 (as amended, the “the Prior NPA”): (i) the $40.0 million aggregate outstanding principal of notes issued March 17, 2014 and due March 17, 2021, and (ii) the $60.0 million aggregate outstanding principal of notes issued November 5, 2015 and due November 5, 2022. In addition, the Company may incur additional senior note indebtedness in an aggregate amount not to exceed $250.0 million. The Credit Facility matures on March 31, 2025 and replaced the Company’s prior $420.0 million credit facility dated March 31, 2016 with Bank of America, N.A., as agent, as amended. All obligations outstanding under the prior credit facility as of the date of the Credit Facility were refinanced by the Credit Facility on March 31, 2020.

On March 31, 2020, the Company entered into an amended and restated Credit Facility Letter Agreement and a Credit Line Note in favor of MUFG Union Bank, N.A., which provides for a $12.0 million line of credit facility related to its cash management services (“Sweep Service Facility”). The Sweep Service Facility matures on the earlier of March 31, 2025, or the date the Company ceases to utilize MUFG Union Bank, N.A. for its cash management services. The Sweep Service Facility replaced the Company’s prior $12.0 million sweep service facility, dated as of March 31, 2016.

At December 31, 2020, under the Credit Facility and Sweep Service Facility, the Company had unsecured lines of credit that permit it to borrow up to $432.0 million of which $122.8 million was outstanding. The Amended Credit Facility contains financial covenants requiring the Company to not (all defined terms used below not otherwise defined herein have the meaning assigned to such terms in the Amended Credit Facility):

Amounts borrowed under the Credit Facility bear interest at the Company’s option at either: (i) LIBOR plus a defined margin, or (ii) the Agent bank’s prime rate (“base rate”) plus a margin. The applicable margin for each type of loan is measured based upon the Consolidated Leverage Ratio at the end of the prior fiscal quarter and ranges from 1.00% to 1.75% for LIBOR loans and 0% to 0.75% for base rate loans. In addition, the Company pays an unused commitment fee for the portion of the $420.0 million credit facility that is not used. These fees are based upon the Consolidated Leverage Ratio and range from 0.15% to 0.30%. As of December 31, 2020 and 2019, the applicable margins were 1.25% for LIBOR based loans, 0.25% for base rate loans and 0.20% for unused fees. Amounts borrowed under the Sweep Service Facility are based upon the MUFG Union Bank, N.A. base rate plus an applicable margin and an unused commitment fee for the portion of the $12.0 million facility not used. The applicable base rate margin and unused commitment fee rates for the Sweep Service Facility are the same as for the Amended Credit Facility. The following information relates to the lines of credit for each of the following periods:

(dollar amounts in thousands)	Year Ended December 31,
	2020			2019
Maximum amount outstanding	$	199,471		$	219,635
Average amount outstanding	$	170,075		$	201,195
Weighted average interest rate, during the period		2.11	%		3.59	%
Prime interest rate, end of period		3.25	%		4.75	%

On March 31, 2020, the Company entered into an Amended and Restated Note Purchase and Private Shelf Agreement (the “Note Purchase Agreement”) with PGIM, Inc. (“PGIM”) and the holders of Series B and Series C Notes previously issued pursuant to the Prior NPA, among the Company and the other parties to the Note Purchase Agreement. The Note Purchase Agreement amended and restated, and superseded in its entirety, the Prior NPA. Pursuant to the Prior NPA, the Company issued (i) $40.0 million aggregate principal amount of its 3.68% Series B Senior Notes due March 17, 2021, and (ii) $60.0 million aggregate principal amount of its 3.84% Series C Senior Notes due November 5, 2022, to which the terms of the Note Purchase Agreement shall apply.

In addition, pursuant to the Note Purchase Agreement, the Company may authorize the issuance and sale of additional senior notes (the “Shelf Notes”) in the aggregate principal amount of (x) $250 million minus (y) the amount of other notes (such as the Series B Senior Notes and Series C Senior Notes, each defined below) then outstanding, to be dated the date of issuance thereof, to mature, in case of each Shelf Note so issued, no more than 15 years after the date of original issuance thereof, to have an average life, in the case of each Shelf Note so issued, of no more than 15 years after the date of original issuance thereof, to bear interest on the unpaid balance thereof from the date thereof at the rate per annum, and to have such other particular terms, as shall be set forth, in the case of each Shelf Note so issued, in accordance with the Note Purchase Agreement. Shelf Notes may be issued and sold from time to time at the discretion of the Company’s Board of Directors and in such amounts as the Board of Directors may determine, subject to prospective purchasers’ agreement to purchase the Shelf Notes. The Company will sell the Shelf Notes directly to such purchasers. The full net proceeds of each Shelf Note will be used in the manner described in the applicable Request for Purchase with respect to such Shelf Note.

On October 1, 2020, the Company entered into a rate lock agreement with Prudential Private Capital, pursuant to which, the Company agreed to a fixed interest rate of 2.57% for future issuance, if any, of senior unsecured notes in the aggregate amount of $40.0 million with a 7-year maturity. If issued, the funding for such notes would occur on or before March 17, 2021 and would be subject to the terms and conditions of the Note Purchase Agreement.

On March 17, 2014, the Company issued and sold to the purchaser a $40.0 million aggregate principal amount of its 3.68% Series B Senior Notes (the “Series B Senior Notes”) pursuant to the terms of the Prior NPA. The Series B Senior Notes are an unsecured obligation of the Company and bear interest at a rate of 3.68% per annum and mature on March 17, 2021. Interest on the Series B Senior Notes is payable semi-annually beginning on September 17, 2014 and continuing thereafter on March 17 and September 17 of each year until maturity. The full net proceeds from the Series B Senior Notes were used for working capital and other general corporate purposes. At December 31, 2020, the principal balance outstanding under the Series B Senior Notes was $40.0 million.

On November 5, 2015, the Company issued and sold to the purchaser a $60.0 million aggregate principal amount of its 3.84% Series C Senior Notes (the “Series C Senior Notes”) pursuant to the terms of the Prior NPA. The Series C Senior Notes are an unsecured obligation of the Company and bear interest at a rate of 3.84% per annum and mature on November 5, 2022. Interest on the Series C Senior Notes is payable semi-annually beginning on May 5, 2016 and continuing thereafter on November 5 and May 5 of each year until maturity. The principal balance is due when the notes mature on November 5, 2022. The full net proceeds from the Series C Senior

Notes were used to reduce the outstanding balance on the Company’s revolving credit line. At December 31, 2020, the principal balance outstanding under the Series C Senior Notes was $60.0 million.

Among other restrictions, the Note Purchase Agreement, under which the Series A Senior Notes, Series B Senior Notes and Series C Senior Notes were sold, contains financial covenants requiring the Company to not (all defined terms used below not otherwise defined herein have the meaning assigned to such terms in the Note Purchase Agreement):

At December 31, 2020, the Company was in compliance with each of the aforementioned covenants. There are no anticipated trends that the Company is aware of that would indicate non-compliance with these covenants, though, significant deterioration in the Company’s financial performance could impact its ability to comply with these covenants.