Debt

Our debt consists of the following (in thousands):



	December 31,
	2012		2011
Debt payable to 2038 at 2.6% to 8.8% in 2012 and 1.5% to 8.8% in 2011	$	2,041,709	$	2,268,668
Unsecured notes payable under credit facilities	66,000		166,500
Debt service guaranty liability	74,075		74,075
Obligations under capital leases	21,000		21,000
Industrial revenue bonds payable to 2015 at 2.4%	1,246		1,594
Total	$	2,204,030	$	2,531,837

The grouping of total debt between fixed and variable-rate as well as between secured and unsecured is summarized below (in thousands):



	December 31,
	2012		2011
As to interest rate (including the effects of interest rate contracts):
Fixed-rate debt	$	1,992,599	$	2,014,834
Variable-rate debt	211,431		517,003
Total	$	2,204,030	$	2,531,837
As to collateralization:
Unsecured debt	$	1,270,742	$	1,510,932
Secured debt	933,288		1,020,905
Total	$	2,204,030	$	2,531,837

Effective September 2011, we entered into an amended and restated $500 million unsecured revolving credit facility. The facility expires in September 2015 and provides for a one-year extension upon our request and borrowing rates that float at a margin over LIBOR plus a facility fee. The borrowing margin and facility fee are priced off a grid that is tied to our senior unsecured credit ratings, which are currently 125 and 25 basis points, respectively. The facility also contains a competitive bid feature that will allow us to request bids for up to $250 million. Additionally, an accordion feature allows us to increase the facility amount up to $700 million.

Effective May 2010, we entered into an agreement with a bank for an unsecured and uncommitted overnight facility totaling $99 million that we intend to maintain for cash management purposes. The facility provides for fixed interest rate loans at a 30 day LIBOR rate plus a borrowing margin based on market liquidity.

The following table discloses certain information regarding our unsecured notes payable under our credit facilities (in thousands, except percentages):



	December 31,
	2012			2011
Unsecured revolving credit facility:
Balance outstanding	$	30,000		$	145,000
Available balance	$	467,571		$	351,571
Letter of credit outstanding under facility	$	2,429		$	3,429
Variable interest rate (excluding facility fee)	1.1		%	1.3		%
Unsecured and uncommitted overnight facility:
Balance outstanding	$	36,000		$	21,500
Variable interest rate	1.5		%	1.5		%
Both facilities:
Maximum balance outstanding during the year	$	303,100		$	330,700
Weighted average balance	$	157,447		$	151,814
Year-to-date weighted average interest rate (excluding facility fee)	1.3		%	1.5		%

Related to a development project in Sheridan, Colorado, we have provided a guaranty for the payment of any debt service shortfalls until a coverage rate of 1.4 is met on tax increment revenue bonds issued in connection with the project. The bonds are to be repaid with incremental sales and property taxes and a PIF to be assessed on current and future retail sales and, to the extent necessary, any amounts we may have to provide under a guaranty. The incremental taxes and PIF are to remain intact until the earlier of the date the bond liability has been paid in full or 2040, as extended by the Agency in April 2011. Therefore, a debt service guaranty liability equal to the fair value of the amounts funded under the bonds was recorded. For both periods ended at December 31, 2012 and 2011, we had $74.1 million outstanding for the debt service guaranty liability.

In November 2012, we redeemed $54.1 million of 3.95% convertible senior unsecured notes due 2026, which were outstanding at December 31, 2011. Interest was payable semi-annually in arrears on February 1 and August 1 of each year.

These notes were originally recorded at a discount, which was amortized through July 2011, resulting in an effective interest rate as of December 31, 2011 of 5.34%.

Net interest expense on our 3.95% convertible senior unsecured notes is as follows (in thousands):



	Year Ended December 31,
	2012		2011		2010
Interest expense	$	1,828	$	4,218	$	5,782
Amortization of discount	—		1,334		2,191
Net interest expense	$	1,828	$	5,552	$	7,973

In October 2012, we issued $300 million of 3.38% senior unsecured notes maturing in 2022. The notes were issued at 99.62% of the principal amount with a yield to maturity of 3.42%. The net proceeds received of $296.9 million were used to reduce amounts outstanding under our $500 million unsecured revolving credit facility and to repay our $54.1 million of 3.95% convertible senior unsecured notes.

In August 2011, we entered into a $200 million unsecured term loan; the proceeds of which were used to repay amounts outstanding under our revolving credit facility. The initial term of the loan was one year, which we repaid at par after nine months on May 31, 2012 at our option. In addition, $180.6 million fixed-rate medium term notes matured during 2012 at a weighted average interest rate of 5.5%.

Various leases and properties, and current and future rentals from those lease and properties, collateralize certain debt. At December 31, 2012 and 2011, the carrying value of such property aggregated $1.5 billion and $1.7 billion, respectively.

Scheduled principal payments on our debt (excluding $66.0 million due under our credit facilities, $21.0 million of certain capital leases, $9.9 million fair value of interest rate contracts, $.9 million net premium/(discount) on debt, $10.2 million of non-cash debt-related items, and $74.1 million debt service guaranty liability) are due during the following years (in thousands):



2013	$	349,108
2014	473,103
2015	274,707
2016	223,198
2017	140,830
2018	63,057
2019 ₍₁₎	152,211
2020	2,099
2021	957
2022	303,410
Thereafter	39,312
Total	$	2,021,992


(1)	Includes $100.0 million of our 8.1% senior unsecured notes due 2019 which may be redeemed by us at any time on or after September 2014 at our option.

Our various debt agreements contain restrictive covenants, including minimum interest and fixed charge coverage ratios, minimum unencumbered interest coverage ratios, minimum net worth requirements and maximum total debt levels. We believe we were in compliance with our public debt and revolving credit facility covenants as of December 31, 2012.