Common Stock and Preferred Stock - Additional Information (Detail) - USD ($)			3 Months Ended		9 Months Ended			12 Months Ended
	Aug. 25, 2017	Jul. 12, 2016	Sep. 30, 2017		Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016		Aug. 31, 2015
Class of Stock [Line Items]
Common Stock, par value			$ 0.01	[1]	$ 0.01	[1]		$ 0.01	[2]
Common Stock, shares authorized			1,917,837,500	[1]	1,917,837,500	[1]		1,945,437,500	[2]
Common Stock, shares issued			1,088,083,794	[1]	1,088,083,794	[1]		1,018,913,249	[2]
Common Stock, shares outstanding			1,088,083,794	[1]	1,088,083,794	[1]		1,018,913,249	[2]
Options exercised under incentive plans, shares					0		0
Direct purchase and dividend reinvestment program - value raised					$ 1,949,000		$ 1,795,000
Direct purchase and dividend reinvestment program - issued shares of common stock					169,000		172,000
Common stock repurchase program, authorized amount										$ 1,000,000,000
Common stock repurchase program, repurchased share					11,132,226
Common stock repurchase program, repurchased value					$ 102,700,000
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					2012-03
Number of common shares authorized for issuance under the Distribution Agency Agreement			125,000,000		125,000,000		125,000,000
Redemption of Series A cumulative preferred stock					$ 185,312,000
IPO [Member]
Class of Stock [Line Items]
Common stock shares issued			60,000,000
Gross proceeds on sale of common stock			$ 709,800,000
Over-Allotment Option
Class of Stock [Line Items]
Gross proceeds on sale of common stock			$ 106,500,000
Stock Issued for underwriter			9,000,000
Hatteras
Class of Stock [Line Items]
Preferred Stock, par value		$ 0.001
Preferred Stock dividend rate, percentage		7.625%
Hatteras | Common Stock
Class of Stock [Line Items]
Business acquisition, shares issued		93,900,000
7.875% Series A Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			7,412,500	[1]	7,412,500	[1]		7,412,500	[2]
Number of shares redeemed	7,412,500
Redemption of Series A cumulative preferred stock	$ 187,500,000				$ 177,088,000
Preferred Stock redeemable price, per share	$ 25.00							$ 25.00
Preferred Stock redemption date					Aug. 25, 2017
Preferred Stock, shares issued			0	[1]	0	[1]		7,412,500	[2]
Preferred Stock, shares outstanding			0	[1]	0	[1]		7,412,500	[2]
Preferred Stock, par value								$ 0.01
Preferred Stock liquidation preference, per share								$ 25.00
Preferred Stock dividend rate, percentage								7.875%
7.625% Series C Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			12,650,000	[1]	12,650,000	[1]		12,650,000	[2]
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00			$ 25.00
Preferred Stock, shares issued			12,000,000	[1]	12,000,000	[1]		12,000,000	[2]
Preferred Stock, shares outstanding			12,000,000	[1]	12,000,000	[1]		12,000,000	[2]
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 redemption period start date					May 16, 2017
7.50% Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			18,400,000	[1]	18,400,000	[1]		18,400,000	[2]
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00			$ 25.00
Preferred Stock, shares issued			18,400,000	[1]	18,400,000	[1]		18,400,000	[2]
Preferred Stock, shares outstanding			18,400,000	[1]	18,400,000	[1]		18,400,000	[2]
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 redemption period start date					Sep. 13, 2017
7.625% Series E Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			11,500,000	[1]	11,500,000	[1]		11,500,000	[2]
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00
Preferred Stock, shares issued			11,500,000	[1]	11,500,000	[1]		11,500,000	[2]
Preferred Stock, shares outstanding			11,500,000	[1]	11,500,000	[1]		11,500,000	[2]
Preferred Stock, par value		$ 0.01	$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share			$ 25.00		$ 25.00
Preferred Stock dividend rate, percentage					7.625%
Preferred Stock redemption period start date					Aug. 27, 2017
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized			32,200,000	[1]	32,200,000	[1]		0	[2]
Preferred Stock redeemable price, per share			$ 25.00		$ 25.00
Preferred Stock, shares issued			28,800,000	[1]	28,800,000	[1]		0	[2]
Preferred Stock, shares outstanding			28,800,000	[1]	28,800,000	[1]		0	[2]
Preferred Stock liquidation preference, per share			$ 25.00		$ 25.00
Preferred Stock dividend rate, percentage					6.95%
Gross proceeds on sale of preferred stock			$ 720,000,000
Cumulative undeclared dividends			$ 8,300,000		$ 8,300,000		$ 0
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock | Commencing from and including the original issue date to, but excluding September 30, 2022
Class of Stock [Line Items]
Preferred Stock liquidation preference, per share			$ 25.00		$ 25.00
Preferred Stock dividend rate, percentage					6.95%
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock | From and including September 30, 2022 | London Interbank Offered Rate (LIBOR)
Class of Stock [Line Items]
Preferred stock floating dividend rate basis					Three-month LIBOR
Preferred stock floating dividend rate spread					4.993%

[1] As a result of a change to a clearing organization's rulebook effective January 3, 2017, beginning with the first quarter 2017 and in subsequent periods the Company is presenting the fair value of centrally cleared interest rate swaps net of variation margin pledged under such transactions. The variation margin was previously reported under cash and cash equivalents and is currently reported as a reduction to interest rate swaps, at fair value. Balances reported prior to the effective date will not be adjusted.

[2] Derived from the audited consolidated financial statements at December 31, 2016.