6. UNSECURED LINE OF CREDIT AND TERM NOTES

Borrowings outstanding on our unsecured line of credit and term notes are as follows:

(Dollars in thousands)	Mar. 31, 2018			Dec. 31, 2017
Revolving line of credit borrowings	$	130,000		$	105,000

Term note due June 4, 2020		100,000			100,000
Term note due August 5, 2021		100,000			100,000
Term note due April 8, 2024		175,000			175,000
Senior term note due July 1, 2026		600,000			600,000
Senior term note due December 15, 2027		450,000			450,000
Term note due July 21, 2028		200,000			200,000
Total term note principal balance outstanding	$	1,625,000		$	1,625,000
Less: unamortized debt issuance costs		(10,612	)		(10,962	)
Less: unamortized senior term note discount		(4,812	)		(4,949	)
Term notes payable	$	1,609,576		$	1,609,089

The Company’s unsecured amended credit agreement includes a revolving credit facility with a limit of $500 million. The interest rate on the revolving credit facility bears interest at a variable annual rate equal to LIBOR plus a margin based on the Company’s credit rating (at March 31, 2018 the margin is 1.10%), and requires an annual 0.15% facility fee. The interest rate at March 31, 2018 on the Company’s line of credit was approximately 2.97% (2.63% at December 31, 2017). At March 31, 2018, there was $369.2 million available on the unsecured revolving line of credit. The revolving line of credit has a maturity date of December 10, 2019. The Company’s unsecured credit agreement also includes an unsecured term note maturing June 4, 2020, which term note was initially in the principal amount of $325 million. In 2017, the Company repaid $225 million under this term note, resulting in $100 million outstanding at March 31, 2018. The term note bears interest at LIBOR plus a margin based on the Company’s credit rating (at March 31, 2018 the margin is 1.15%). The interest rate at March 31, 2018 on the term note was approximately 2.84% (2.53% at December 31, 2017).

On December 7, 2017, the Operating Partnership issued $450 million in aggregate principal amount of 3.875% unsecured senior notes due December 15, 2027 (the “2027 Senior Notes”). The 2027 Senior Notes were issued at a 0.477% discount to par value. Interest on the 2027 Senior Notes is payable semi-annually on each June 15 and December 15, beginning on June 15, 2018. The 2027 Senior Notes are fully and unconditionally guaranteed by the Parent Company. Proceeds received upon issuance, net of discount to par of $2.1 million and underwriting discount and other offering expenses of $4.0 million, totaled $443.9 million.

On June 20, 2016, the Operating Partnership issued $600 million in aggregate principal amount of 3.50% unsecured senior notes due July 1, 2026 (the “2026 Senior Notes”). The 2026 Senior Notes were issued at a 0.553% discount to par value. Interest on the 2026 Senior Notes is payable semi-annually in arrears on each January 1 and July 1. The 2026 Senior Notes are fully and unconditionally guaranteed by the Parent Company. Proceeds received upon issuance, net of discount to par of $3.3 million and underwriting discount and other offering expenses of $5.5 million, totaled $591.2 million.

The indenture under which the 2027 Senior Notes and the 2026 Senior Notes were issued restricts the ability of the Company and its subsidiaries to incur debt unless the Company and its consolidated subsidiaries comply with a leverage ratio not to exceed 60% and an interest coverage ratio of more than 1.5:1 on all outstanding debt, after giving effect to the incurrence of the debt. The indenture also restricts the ability of the Company and its subsidiaries to incur secured debt unless the Company and its consolidated subsidiaries comply with a secured debt leverage ratio not to exceed 40% after giving effect to the incurrence of the debt. The indenture also contains other financial and customary covenants, including a covenant not to own unencumbered assets with a value less than 150% of the unsecured indebtedness of the Company and its consolidated subsidiaries. At March 31, 2018, the Company was in compliance with such covenants.

On July 21, 2016, the Company entered into a $200 million term note maturing July 21, 2028 bearing interest at a fixed rate of 3.67%.

On April 8, 2014, the Company entered into a $175 million term note maturing April 8, 2024 bearing interest at a fixed rate of 4.533%. The interest rate on the term note increases to 6.283% if the Company is not rated by at least one rating agency or if the Company’s credit rating is downgraded.

In 2011, the Company entered into a $100 million term note maturing August 5, 2021 bearing interest at a fixed rate of 5.54%. The interest rate on the term note increases to 7.29% if the notes are not rated by at least one rating agency, the credit rating on the notes is downgraded or if the Company’s credit rating is downgraded.

The line of credit and term notes require the Company to meet certain financial covenants, measured on a quarterly basis, including prescribed leverage, fixed charge coverage, minimum net worth, limitations on additional indebtedness and limitations on dividend payouts. At March 31, 2018, the Company was in compliance with such covenants.

We believe that if operating results remain consistent with historical levels and levels of other debt and liabilities remain consistent with amounts outstanding at March 31, 2018, the entire availability on the line of credit could be drawn without violating our debt covenants.

The Company’s fixed rate term notes contain a provision that allows for the noteholders to call the debt upon a change of control of the Company at an amount that includes a make whole premium based on rates in effect on the date of the change of control.

Deferred debt issuance costs and the discount on the outstanding term notes are both presented as reductions of term notes in the accompanying consolidated balance sheets at March 31, 2018 and December 31, 2017. Amortization expense related to these deferred debt issuance costs was $0.5 million and $0.5 million for the three months ended March 31, 2018 and 2017, respectively, and is included in interest expense in the consolidated statements of operations.