DECEMBER 31	2019			2018
(in millions)
Senior debentures maturing April 15, 2026	$	375.0		$	375.0
Senior debentures maturing October 15, 2025		62.6			62.6
Subordinated debentures maturing March 30, 2053		175.0			175.0
Subordinated debentures maturing February 3, 2027		50.1			50.1
FHLB borrowings (secured)		—			125.0
Total principal debt		662.7			787.7
Unamortized debt issuance costs		(9.3	)		(9.8	)
Total	$	653.4		$	777.9

The Company has outstanding 7.625% unsecured senior debentures with a par value of $62.6 million as of December 31, 2019 and 2018 and mature on October 15, 2025. Additionally, the Company has outstanding unsecured senior debentures that were issued on April 8, 2016 with a par value of $375.0 million, as of December 31, 2019 and 2018 and mature on April 15, 2026. Both of the Company’s outstanding senior debentures are subject to certain restrictive covenants, including limitations on the issuance or disposition of stock of restricted subsidiaries and limitations on liens, and pay interest semi-annually.

The Company has outstanding $175.0 million aggregate principal amount of 6.35% subordinated unsecured debentures due March 30, 2053. These debentures pay interest quarterly. The Company may redeem these debentures in whole at any time, or in part from time to time, on or after March 30, 2018, at a redemption price equal to their principal amount plus accrued and unpaid interest. In addition, the Company’s subordinated debentures maturing February 3, 2027 have a par value of $50.1 million as of December 31, 2019 and 2018 and pay cumulative dividends semi-annually at 8.207%.

On January 2, 2019, the Company repaid $125.0 million of its FHLB advances that were due 2029 and had an interest rate of 5.5%, along with related prepayment fees of $26 million; such fees were recognized in 2018. Membership in FHLB provides the Company with access to additional short-term liquidity based on the level of investment in FHLB stock and pledged collateral. Total holdings of FHLB stock were $2.1 million and $8.7 million at December 31, 2019 and 2018, respectively. At December 31, 2019, the Company had pledged government agency securities with a fair value of $94.0 million as collateral for periodic short-term borrowings with the FHLB. Additionally, at December 31, 2018, the Company had pledged government agency securities with a fair value of $234.9

million in support of the $125.0 million advance that was repaid on January 2, 2019, and for periodic short-term borrowings. There were no borrowings outstanding with the FHLB at December 31, 2019 or 2018.

At December 31, 2019, the Company had a $200.0 million credit agreement which expires in April 2024. The Company had no borrowings under this agreement as of December 31, 2019.

Interest expense was $37.5 million, $45.1 million, and $45.2 million in 2019, 2018 and 2017, respectively. At December 31, 2019, the Company was in compliance with the covenants associated with all of its debt indentures and credit arrangements.