Senior Unsecured Notes and Secured Debt (Details) £ in Thousands, CAD in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2016 CAD	Dec. 31, 2016 GBP (£)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 01, 2015 USD ($)
Principal payments due on debt obligations
2017				$ 550,620
2018				1,147,557
2019				1,228,753
2020	[1]			840,379
2021	[2],[3]			1,485,312
Thereafter	[4],[5],[6],[7]			6,472,483
Totals				11,725,104
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Senior unsecured notes				8,161,619	$ 8,548,055
Secured debt				3,477,699	$ 3,509,142
Debt instrument maturity date		May 13, 2021
Senior Unsecured Notes [Member]
Principal payments due on debt obligations
2017	[8],[9]			0
2018	[8],[9]			450,000
2019	[8],[9]			605,000
2020	[1],[8],[9]			673,447
2021	[2],[3],[8],[9]			1,136,206
Thereafter	[4],[5],[6],[7],[8],[9]			5,395,385
Totals	[8],[9]			$ 8,260,038
Senior Unsecured Notes [Member] | Maximum [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		1.40%	1.40%	1.40%
Senior Unsecured Notes [Member] | Minimum [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		6.50%	6.50%	6.50%
Secured Debt [Member]
Principal payments due on debt obligations
2017	[8],[10]			$ 550,620
2018	[8],[10]			697,557
2019	[8],[10]			623,753
2020	[1],[8],[10]			166,932
2021	[2],[3],[8],[10]			349,106
Thereafter	[4],[5],[6],[7],[8],[10]			1,077,098
Totals	[8],[10]			3,465,066
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Carrying values of properties securing the debt				$ 6,149,872
Secured Debt [Member] | Maximum [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		1.24%	1.24%	1.24%
Secured Debt [Member] | Minimum [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		7.98%	7.98%	7.98%
Canadian Denominated Unsecured Term Loan [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		1.84%
Senior unsecured notes		CAD 250,000		$ 186,206
Interest Rate margin		0.95%
Debt Instrument, Issuance Date		May 13, 2016
Debt instrument maturity date		May 13, 2021
Unsecured Line of Credit Term Loan [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		1.63%
Senior unsecured notes				500,000
Interest Rate margin		0.95%
Debt Instrument, Issuance Date		May 13, 2016
Debt instrument maturity date		May 13, 2021
3.35% Canadian Senior Secured Note Due 2020 [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		3.35%
Senior unsecured notes		CAD 300,000		223,447
Debt Instrument, Issuance Date		Nov. 01, 2015
Debt instrument maturity date		Nov. 01, 2020
Uk Debt Due 2028 [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		4.80%
Senior unsecured notes			£ 550,000	678,535
Debt Instrument, Issuance Date		Nov. 20, 2013
Debt instrument maturity date		Nov. 20, 2028
Uk Debt Due 2034 [Member]
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		4.50%
Senior unsecured notes			£ 500,000	616,850
Debt Instrument, Issuance Date		Nov. 25, 2014
Debt instrument maturity date		Nov. 25, 2034
4.00% Senior Unsecured Notes Due 2025
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		4.00%
Senior unsecured notes				750,000
Debt Instrument, Issuance Date		May 01, 2015
Debt instrument maturity date		May 01, 2025
Senior Unsecured Notes Additional Issued Amount						$ 500,000
4.25% Senior Unsecured Notes Due 2026
Senior Unsecured Notes and Secured Debt Textual [Abstract]
Interest rate		4.25%
Senior unsecured notes issued amount				$ 700,000
Debt Instrument, Issuance Date		Mar. 01, 2016
Debt instrument maturity date		Mar. 01, 2026

[1] In November 2015, one of our wholly-owned subsidiaries issued and we guaranteed $300,000,000 of Canadian-denominated 3.35% senior unsecured notes due 2020 (approximately $223,447,000 based on the Canadian/U.S. Dollar exchange rate on December 31, 2016).

[2] On May 13, 2016, we refinanced the funding on a $250,000,000 Canadian-denominated unsecured term credit facility (approximately $186,206,000 based on the Canadian/U.S. Dollar exchange rate on December 31, 2016). The loan matures on May 13, 2021 and bears interest at the Canadian Dealer Offered Rate plus 95 basis points (1.84% at December 31, 2016).

[3] On May 13, 2016, we refinanced the funding on a $500,000,000 unsecured term credit facility. The loan matures on May 13, 2021 and bears interest at LIBOR plus 95 basis points (1.63% at December 31, 2016).

[4] In March 2016, we issued $700,000,000 of 4.25% senior unsecured notes due 2026.

[5] In May 2015, we issued $750,000,000 of 4.0% senior unsecured notes due 2025. In October 2015, we issued an additional $500,000,000 of these notes under a re-opening of the offer.

[6] On November 20, 2013, we completed the sale of £550,000,000 (approximately $678,535,000 based on the Sterling/U.S. Dollar exchange rate in effect on December 31, 2016) of 4.8% senior unsecured notes due 2028.

[7] On November 25, 2014, we completed the sale of £500,000,000 (approximately $616,850,000 based on the Sterling/U.S. Dollar exchange rate in effect on December 31, 2016) of 4.5% senior unsecured notes due 2034.

[8] Amounts represent principal amounts due and do not include unamortized premiums/discounts, debt issuance costs, or other fair value adjustments as reflected on the consolidated balance sheet.

[9] Annual interest rates range from 1.4% to 6.5%.

[10] Annual interest rates range from 1.24% to 7.98%. Carrying value of the properties securing the debt totaled $6,149,872,000 at December 31, 2016.