8. Notes Payable

The following is a summary of our indebtedness:



(in millions)	June 30, 2018		December 31, 2017
Senior unsecured notes (1)
4.78% Notes, due 2021	$	248.9	$	248.7
3.15% Notes, due 2022	347.0		346.6
5.07% Notes, due 2023	247.8		247.6
4.36% Notes, due 2024	248.6		248.5
3.68% Notes, due 2024	247.4		247.2
	$	1,339.7	$	1,338.6

Secured notes (1)
2.62% – 5.77% Conventional Mortgage Notes, due 2018 – 2045	$	865.6	$	866.0

Total notes payable	$	2,205.3	$	2,204.6

Other floating rate debt included in secured notes (2.62%)	$	175.0	$	175.0


(1)	Unamortized debt discounts and debt issuance costs of $10.9 million and $12.3 million are included in senior unsecured and secured notes payable as of June 30, 2018 and December 31, 2017, respectively.

We have a $600 million unsecured credit facility which matures in August 2019, with two six-month options to extend the maturity date at our election to August 2020. Additionally, we have the option to further increase our credit facility to $900 million by either adding additional banks to the facility or obtaining the agreement of the existing banks to increase their commitments. The interest rate on our credit facility is based upon the London Interbank Offered Rate ("LIBOR") plus a margin which is subject to change as our credit ratings change. Advances under our credit facility may be priced at the scheduled rates, or we may enter into bid rate loans with participating banks at rates below the scheduled rates. These bid rate loans have terms of 180 days or less and may not exceed the lesser of $300 million or the remaining amount available under our credit facility. Our credit facility is subject to customary financial covenants and limitations. We believe we are in compliance with all such financial covenants and limitations on the date of this filing.

Our credit facility provides us with the ability to issue up to $50 million in letters of credit. While our issuance of letters of credit does not increase our borrowings outstanding under our credit facility, it does reduce the amount available. At June 30, 2018, we had no balances outstanding on our $600 million credit facility and we had outstanding letters of credit totaling approximately $12.6 million, leaving approximately $587.4 million available under our credit facility.

In May 2018, we extended the term on our $45.0 million unsecured short-term borrowing facility from May 2018 to May 2019. The interest rate is based on LIBOR plus 0.95%. At June 30, 2018, we had no balances outstanding on this unsecured short-term borrowing facility, leaving $45.0 million available under this facility.

We had outstanding floating rate debt of approximately $175.0 million and $275.0 million at June 30, 2018 and 2017, respectively, which included amounts borrowed under our unsecured credit facility and unsecured short-term borrowings. The weighted average interest rate on such debt was approximately 2.6% and 1.8% for the six months ended June 30, 2018 and 2017, respectively.

Our indebtedness had a weighted average maturity of approximately 3.8 years at June 30, 2018. The table below is a summary of the maturity dates of our outstanding debt and principal amortizations, and the weighted average interest rates on such debt, at June 30, 2018:



(in millions) (1)	Amount			Weighted Average Interest Rate
2018	$	174.4		2.6	%
2019	643.0			5.4
2020 (2)	(1.2		)	—
2021	249.1			4.8
2022	349.3			3.2
Thereafter	790.7			4.4
Total	$	2,205.3		4.4	%


(1)	Includes all available extension options.


(2)	Includes amortization of debt discounts and debt issuance costs, net of scheduled principal payments.