9. Notes Payable

The following is a summary of our indebtedness:



	December 31,
(in millions)	2016		2015
Commercial banks
Unsecured credit facility	$	—	$	225.0
Unsecured short-term borrowings	—		19.0
	$	—	$	244.0

Senior unsecured notes (1)
5.83% Notes, due 2017	$	246.6	$	246.3
4.78% Notes, due 2021	248.4		248.0
3.15% Notes, due 2022	346.0		345.4
5.07% Notes, due 2023	247.2		246.8
4.36% Notes, due 2024	248.2		248.0
3.68% Notes, due 2024	246.8		246.4
	$	1,583.2	$	1,580.9

Total unsecured notes payable	1,583.2		1,824.9

Secured notes (1)
1.25% – 5.77% Conventional Mortgage Notes, due 2018 – 2045	866.7		867.4
Tax-exempt Mortgage Note, originally due 2028 (2.18% floating rate)	30.7		32.4
	897.4		899.8
Total notes payable	$	2,480.6	$	2,724.7

Other floating rate debt included in secured notes (1.25%)	$	175.0	$	175.0
Value of real estate assets, at cost, subject to secured notes	$	1,598.9	$	1,568.9


(1)	Unamortized debt discounts and debt issuance costs of $15.7 million and $18.6 million are included in senior unsecured and secured notes payable as of December 31, 2016 and 2015, respectively.

In August 2015, we amended and restated our $500 million unsecured credit facility, which extended the maturity date from September 2015 to August 2019, with two six-month options to extend the maturity date at our election to August 2020, and increased the availability to $600 million, with the option to further increase it 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 this 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 this 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 the credit facility. This 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 December 31, 2016, we had no balances outstanding on our $600 million credit facility and we had outstanding letters of credit totaling approximately $12.7 million, leaving approximately $587.3 million available under our credit facility.

At December 31, 2016 and 2015, we had outstanding floating rate debt of approximately $205.7 million and $451.4 million, respectively, which included our unsecured credit facility and unsecured short-term borrowings, and the weighted average interest rate on this debt was approximately 1.4% and 1.2% for the years ended December 31, 2016 and 2015, respectively.

Our indebtedness, which includes our unsecured credit facility, had a weighted average maturity of 4.9 years at December 31, 2016. 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 December 31, 2016:



(in millions)	Amount			Weighted Average Interest Rate
2017 (1)	$	276.0		5.4	%
2018	173.8			1.2
2019	643.2			5.4
2020 (2)	(1.1		)	—
2021	249.1			4.8
Thereafter (1)	1,139.6			4.0
Total	$	2,480.6		4.4	%


(1)	Subsequent to December 31, 2016, we gave notice of advance repayment on our tax-exempt secured note payable of approximately $30.7 million in February 2017, which was initially due to mature in 2028. This table reflects this repayment in 2017.


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