7. Notes Payable

The following is a summary of our indebtedness:



(in millions)	March 31, 2015		December 31, 2014
Senior unsecured notes
5.08% Notes, due 2015	$	249.9	$	249.9
5.75% Notes, due 2017	246.5		246.5
4.70% Notes, due 2021	249.0		249.0
3.07% Notes, due 2022	347.1		347.0
5.00% Notes, due 2023	247.9		247.8
4.27% Notes, due 2024	249.6		249.6
3.59% Notes, due 2024	248.2		248.1
	$	1,838.2	$	1,837.9

Secured notes
0.95% – 5.63% Conventional Mortgage Notes, due 2018 – 2045	870.6		870.9
Tax-exempt Mortgage Note, due 2028 (1.26% floating rate)	34.3		34.7
	904.9		905.6
Total notes payable	$	2,743.1	$	2,743.5

Other floating rate debt included in secured notes (0.95%)	$	175.0	$	175.0

We have a $500 million unsecured credit facility which matures in September 2015 with an option to extend at our election to September 2016. Additionally, we have the option to increase this credit facility to $750 million by either adding additional banks to the credit facility or obtaining the agreement of the existing banks in the credit facility to increase their commitments. The interest rate is based upon the London Interbank Offered Rate ("LIBOR") plus a margin which is subject to change as our credit ratings change. Advances under the line of credit 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 $250 million or the remaining amount available under the line of credit. The line of credit 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 line of credit provides us with the ability to issue up to $100 million in letters of credit. While our issuance of letters of credit does not increase our borrowings outstanding under our line of credit, it does reduce the amount available. At March 31, 2015, we had no balance outstanding on our $500 million unsecured line of credit and we had outstanding letters of credit totaling approximately $6.4 million, leaving approximately $493.6 million available under our unsecured line of credit.

At March 31, 2015 and 2014, we had outstanding floating rate debt of approximately $209.4 million and $270.9 million, respectively, which includes our unsecured line of credit and short-term borrowings, and the weighted average interest rate on such debt was approximately 1.0% for each of the three months ended March 31, 2015 and 2014.

Our indebtedness had a weighted average maturity of 6.1 years at March 31, 2015. Set forth 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 March 31, 2015, were as follows:



(in millions)	Amount		Weighted Average Interest Rate
2015	$	251.4	5.1	%
2016 (1)	2.0		—
2017	249.0		5.8
2018	177.4		1.0
2019	646.5		5.3
Thereafter	1,416.8		4.0
Total	$	2,743.1	4.4	%


(1)	Includes only scheduled principal amortizations.