We may repurchase, redeem or refinance convertible and non-convertible senior unsecured notes from time to time, taking advantage of favorable market conditions when available. We may purchase senior notes for cash through open market purchases, privately negotiated transactions, a tender offer or, in some cases, through the early redemption of such securities pursuant to their terms. The non-convertible senior unsecured notes are redeemable at our option, at any time in whole or from time to time in part, at a redemption price equal to the sum of (1) the principal amount of the notes (or portion of such notes) being redeemed plus accrued and unpaid interest thereon up to the redemption date and (2) any “make-whole” amount due under the terms of the notes in connection with early redemptions. Redemptions and repurchases of debt, if any, will depend on prevailing market conditions, our liquidity requirements, contractual restrictions and other factors. At December 31, 2012, the annual principal payments due on these debt obligations were as follows (in thousands):

	Senior		Secured
	Unsecured Notes^(1,2)		Debt ^(1,3)		Totals
2013	$	300,000	$	110,034	$	410,034
2014		0		204,783		204,783
2015⁽⁴⁾		501,054		224,486		725,540
2016		700,000		328,730		1,028,730
2017		450,000		320,943		770,943
Thereafter		4,194,403		1,122,610		5,317,013
Totals	$	6,145,457	$	2,311,586	$	8,457,043


(1) Amounts represent principal amounts due and do not include unamortized premiums/discounts or other fair value adjustments as reflected on the consolidated balance sheet.
(2) Annual interest rates range from 2.25% to 6.5%, excluding the Canadian denominated unsecured term loan.
(3) Annual interest rates range from 1.0% to 10.0%. Carrying value of the properties securing the debt totaled $3,953,516,000 at December 31, 2012.
(4) On July 30, 2012, we completed funding on a $250,000,000 Canadian denominated unsecured term loan (approximately $251,054,000 USD at exchange rates on December 31, 2012). The loan matures on July 27, 2015 (with an option to extend for an additional year at our discretion) and bears interest at the Canadian Dealer Offered Rate plus 145 basis points (2.67% at December 31, 2012).

During the twelve months ended December 31, 2010, we issued $494,403,000 of 3.00% senior unsecured convertible notes due December 2029, generating net proceeds of $486,084,000. The notes are convertible, in certain circumstances, into cash and, if applicable, shares of common stock at an initial conversion rate of 19.5064 shares per $1,000 principal amount of notes, which represents an initial conversion price of $51.27 per share. In general, upon conversion, the holder of each note would receive, in respect of the conversion value of such note, cash up to the principal amount of such note and common stock for the note's conversion value in excess of such principal amount. In addition, on each of December 1, 2014, December 1, 2019 and December 1, 2024, holders may require us to purchase all or a portion of their notes at a purchase price in cash equal to 100% of the principal amount of the notes to be purchased, plus any accrued and unpaid interest. The notes are bifurcated into a debt component and an equity component since they may be settled in cash upon conversion. The value of the debt component is based upon the estimated fair value of a similar debt instrument without the conversion feature at the time of issuance. The difference between the contractual principal on the debt and the value allocated to the debt of $29,925,000 was recorded as an equity component and represents the conversion feature of the instrument. The excess of the contractual principal amount of the debt over its estimated fair value is amortized to interest expense using the effective interest method over the period used to estimate the fair value.

The following is a summary of our senior unsecured note principal activity, excluding the Canadian denominated unsecured term loan, during the periods presented (dollars in thousands):

	Year Ended
	December 31, 2012			December 31, 2011			December 31, 2010
			Weighted Avg.			Weighted Avg.			Weighted Avg.
	Amount		Interest Rate	Amount		Interest Rate	Amount		Interest Rate

Beginning balance	$	4,464,927	5.133%	$	3,064,930	5.129%	$	1,661,853	5.557%
Debt issued		1,800,000	3.691%		1,400,000	5.143%		1,844,403	4.653%
Debt extinguished		(76,853)	8.000%		(3)	4.750%		(441,326)	4.750%
Debt redeemed		(293,671)	4.750%		-	0.000%		-	0.000%
Ending balance	$	5,894,403	4.675%	$	4,464,927	5.133%	$	3,064,930	5.129%

The following is a summary of our secured debt principal activity for the periods presented (dollars in thousands):

	Year Ended
		December 31, 2012		December 31, 2011			December 31, 2010
			Weighted Avg.			Weighted Avg.			Weighted Avg.
	Amount		Interest Rate	Amount		Interest Rate	Amount		Interest Rate
Beginning balance	$	2,108,384	5.285%	$	1,133,715	5.972%	$	623,045	5.842%
Debt issued		157,418	4.212%		116,903	5.697%		157,156	5.454%
Debt assumed		444,744	5.681%		940,854	4.444%		564,656	6.089%
Debt extinguished		(360,403)	4.672%		(55,317)	5.949%		(194,493)	6.073%
Foreign currency		187	5.637%		-	0.000%		-	0.000%
Principal payments		(38,744)	5.456%		(27,771)	5.845%		(16,649)	5.792%
Ending balance	$	2,311,586	5.140%	$	2,108,384	5.285%	$	1,133,715	5.972%

Our debt agreements contain various covenants, restrictions and events of default. Certain agreements require us to maintain certain financial ratios and minimum net worth and impose certain limits on our ability to incur indebtedness, create liens and make investments or acquisitions. As of December 31, 2012, we were in compliance with all of the covenants under our debt agreements.