Senior Unsecured Notes and Secured Debt (Details)	12 Months Ended
	Dec. 31, 2014 USD ($)		Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2010 3.00% senior unsecured convertible notes due December 2029 USD ($)	Dec. 31, 2014 3.00% senior unsecured convertible notes due December 2029 Conversion Notice 1 [Member] USD ($)	Dec. 31, 2014 3.00% senior unsecured convertible notes due December 2029 Conversion Notice 2 [Member] USD ($)	Dec. 31, 2010 3.00% senior unsecured convertible notes due December 2029 Debt Instrument Redemption Period One [Member]	Dec. 31, 2010 3.00% senior unsecured convertible notes due December 2029 Debt Instrument Redemption Period Two [Member]	Dec. 31, 2014 Senior Unsecured Notes [Member] USD ($)		Dec. 31, 2013 Senior Unsecured Notes [Member] USD ($)	Dec. 31, 2014 Secured Debt [Member] USD ($)		Dec. 31, 2014 Canadian Term Loan [Member] USD ($)	Dec. 31, 2014 Canadian Term Loan [Member] CAD	Dec. 31, 2014 Unsecured Term Loan [Member] USD ($)	Dec. 31, 2014 Unsecured Notes England [Member] USD ($)	Dec. 31, 2014 Unsecured Notes England [Member] GBP (£)	Dec. 31, 2013 Unsecured Notes England [Member] USD ($)	Dec. 31, 2013 Unsecured Notes England [Member] GBP (£)
Principal payments due on debt obligations
2015	$ 399,813,000										$ 0	[1],[2]		$ 399,813,000	[1],[3]
2016	1,112,248,000										700,000,000	[1],[2]		412,248,000	[1],[3]
2017	808,023,000										450,000,000	[1],[2]		358,023,000	[1],[3]
2018	886,884,000										450,000,000	[1],[2]		436,884,000	[1],[3]
2019	1,685,571,000	[4],[5]									1,315,499,000	[1],[2],[4],[5]		370,072,000	[1],[3],[4],[5]
Thereafter	5,866,380,000	[6],[7]									4,901,655,000	[1],[2],[6],[7]		964,725,000	[1],[3],[6],[7]
Totals	10,758,919,000										7,817,154,000	[1],[2]		2,941,765,000	[1],[3]
Senior Unsecured Convertible Notes Issued [Abstract]
Convertible Debt Issued Amount					494,403,000
Proceeds from issuance of senior unsecured convertible notes					486,084,000								219,925,000
Debt Instrument Issuance Date 1						Dec. 31, 2010										Jul. 25, 2014	Jul. 25, 2014	Jul. 25, 2014	Nov. 25, 2014	Nov. 25, 2014	Nov. 20, 2013	Nov. 20, 2013
Debt Instrument, Face Amount						494,403,000
Debt Instrument Interest Rate Stated Percentage						3.00%
Conversion rate						19.5064
Conversion price						$ 51.27
Equity component of convertible debt, reacquire	1,193,000			3,275,000		29,925,000
Repurchase Date									Dec. 01, 2019	Dec. 01, 2024
Repurchase Percentage						100.00%
Debt Conversion Amount							59,143,000	142,238,000
Conversion Share Amount							258,542
Gains (Losses) on Extinguishment of Debt	(9,558,000)		909,000	775,000			974,000						2,423,000
Debt Conversion, Converted Instrument, Settlement Date								Mar. 31, 2015
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Notes, annual stated interest rates, Minimum											1.32%			1.00%
Notes, annual stated interest rates, Maximum											6.50%			7.98%
Par value of senior debt						494,403,000
Issuance Date						Dec. 31, 2010										Jul. 25, 2014	Jul. 25, 2014	Jul. 25, 2014	Nov. 25, 2014	Nov. 25, 2014	Nov. 20, 2013	Nov. 20, 2013
Secured debt	2,977,713,000		3,058,248,000
Carrying values of properties securing the debt	5,424,956,000
Unsecured debt	7,766,251,000		7,379,308,000													215,498,664	250,000,000	500,000,000	781,900,000	500,000,000	853,790,000	550,000,000
Applicable margin over index, based on certain debt ratings	1.15%															1.15%	1.15%	1.15%
Senior note conversions	258,542		988,007	1,039,721
Loss (gain) on extinguishment of senior unsecured convertible notes	$ (9,558,000)		$ 909,000	$ 775,000			$ 974,000						$ 2,423,000
Interest Rate																2.40%	2.40%	1.32%	4.50%	4.50%	4.80%	4.80%
Maturity Date	Oct. 31, 2018															Oct. 31, 2018	Oct. 31, 2018	Oct. 31, 2018	Jan. 01, 2034	Jan. 01, 2034	Jan. 01, 2028	Jan. 01, 2028

[1] (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] (2) Annual interest rates range from 1.32% to 6.5%.

[3] (3) Annual interest rates range from 1.0% to 7.98%. Carrying value of the properties securing the debt totaled $5,424,956,000 at December 31, 2014.

[4] (4) On July 25, 2014, we refinanced the funding on a $250,000,000 Canadian-denominated unsecured term credit facility (approximately $215,498,664 based on the Canadian/U.S. Dollar exchange rate on December 31, 2014). The loan matures on October 31, 2018 (with an option to extend for an additional year at our discretion) and bears interest at the Canadian Dealer Offered Rate plus 115 basis points (2.4% at December 31, 2014).

[5] (5) On July 25, 2014, we refinanced the funding on a $500,000,000 unsecured term credit facility. The loan matures on October 31, 2018 (with an option to extend for one additional year at our discretion) and bears interest at LIBOR plus 115 basis points (1.32% at December 31, 2014).

[6] (6) On November 20, 2013, we completed funding on £550,000,000 (approximately $853,790,000 based on the Sterling/U.S. Dollar exchange rate on December 31, 2014) of 4.8% senior unsecured notes due 2028.

[7] (7) On November 25, 2014, we completed funding on £500,000,000 (approximately $781,900,000 based on the Sterling/U.S. Dollar exchange rate on December 31, 2014) of 4.5% senior unsecured notes due 2034.