Common Stock and Preferred Stock - Narrative (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 30, 2015	Oct. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Class of Stock [Line Items]
Common Stock, par value			$ 0.01		$ 0.01		$ 0.01	[1]
Common Stock, shares authorized			1,956,937,500		1,956,937,500		1,956,937,500	[1]
Common Stock, shares issued			947,826,176		947,826,176		947,643,079	[1]
Common Stock, shares outstanding			947,826,176		947,826,176		947,643,079	[1]
Options exercised under incentive plans, shares					0	0
Direct purchase and dividend reinvestment program - value raised					$ 1,724	$ 1,786
Direct purchase and dividend reinvestment program - issued shares					168,000	159,000
Description of common stock equity distribution agreement					In March 2012, the Company entered into six separate Distribution Agency Agreements ("Distribution Agency Agreements") with each of Merrill Lynch; Pierce, Fenner & Smith Incorporated; Credit Suisse Securities (USA) LLC; Goldman, Sachs & Co.; J.P. Morgan Securities LLC; Morgan Stanley & Co. LLC; and RCap Securities, Inc. (together, the Agents).
Date of Distribution Agency Agreement with six separate Agents					March 2012
Number of common shares authorized for issuance under the Distribution Agency Agreement			125,000,000	125,000,000	125,000,000	125,000,000
Common stock - dividend declared					$ 852,989	$ 852,786
Dividends payable, date to be paid					Oct. 30, 2015	Jul. 29, 2014
Dividends declared per share of common stock			$ 0.30	$ 0.30	$ 0.90	$ 0.90
Payment to dividends		$ 284,300			$ 906,910	$ 906,714
Payment to dividends, per share		$ 0.30
Subsequent Event
Class of Stock [Line Items]
Payment to dividends	$ 284,300
Payment to dividends, per share	$ 0.30
7.625% Series C Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			12,650,000		12,650,000		12,650,000	[1]
Preferred Stock, shares issued			12,000,000		12,000,000		12,000,000	[1]
Preferred Stock, shares outstanding			12,000,000		12,000,000		12,000,000	[1]
Preferred Stock, par value			$ 0.01		$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share			25.00		$ 25.00		$ 25.00
Preferred Stock dividend rate, percentage					7.625%		7.625%
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00		$ 25.00
Preferred Stock redemption date					May 16, 2017
Preferred dividends declared					$ 17,157	$ 17,157
Preferred series dividends declared, per share					$ 1.430	$ 1.430
7.50% Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			18,400,000		18,400,000		18,400,000	[1]
Preferred Stock, shares issued			18,400,000		18,400,000		18,400,000	[1]
Preferred Stock, shares outstanding			18,400,000		18,400,000		18,400,000	[1]
Preferred Stock, par value			$ 0.01		$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share			25.00		$ 25.00		$ 25.00
Preferred Stock dividend rate, percentage					7.50%		7.50%
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00		$ 25.00
Preferred Stock redemption date					Sep. 13, 2017
Preferred dividends declared					$ 25,875	$ 25,875
Preferred series dividends declared, per share					$ 1.406	$ 1.406
7.875% Series A Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			7,412,500		7,412,500		7,412,500	[1]
Preferred Stock, shares issued			7,412,500		7,412,500		7,412,500	[1]
Preferred Stock, shares outstanding			7,412,500		7,412,500		7,412,500	[1]
Preferred Stock, par value			$ 0.01		$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share			25.00		$ 25.00		$ 25.00
Preferred Stock dividend rate, percentage					7.875%		7.875%
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00		$ 25.00
Preferred Stock redemption date					Apr. 05, 2009
Preferred dividends declared					$ 10,944	$ 10,944
Preferred series dividends declared, per share					$ 1.477	$ 1.477
6.00% Series B Cumulative Convertible Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			4,600,000		4,600,000

[1] Derived from the audited consolidated financial statements at December 31, 2014.