Subsequent Events - Additional Information (Detail) - USD ($)					6 Months Ended
	Jul. 31, 2017	Jul. 27, 2017	Jul. 26, 2017	Jul. 21, 2017	Jun. 30, 2017	Aug. 03, 2017	Dec. 31, 2016
7.875% Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Preferred stock, redemption price					$ 25.00		$ 25.00
Redemption date					Apr. 05, 2009
Pingora Holdings, L.P.
Subsequent Event [Line Items]
Date of disposal agreement					Jul. 10, 2017
Subsequent Event
Subsequent Event [Line Items]
Common stock shares issued				60,000,000
Gross proceeds on sale of common stock				$ 710,000,000
Credit facility agreement by a wholly owned subsidiary			$ 150,000,000
Credit facility agreement by a wholly owned subsidiary, outstanding balance						$ 0
Subsequent Event | 7.875% Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Number of shares for which notice is provided for redemptions			7,412,500
Preferred stock, redemption price			$ 25
Redemption date			Aug. 25, 2017
Subsequent Event | 6.00% Series B Cumulative Convertible Preferred Stock
Subsequent Event [Line Items]
Number of shares reclassified and designated as common stock		4,600,000
Subsequent Event | 6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Gross proceeds on sale of common stock	$ 700,000,000
Preferred stock shares issued	$ 28,000,000
Subsequent Event | Over-Allotment Option
Subsequent Event [Line Items]
Gross proceeds on sale of common stock			$ 106,000,000
Stock Issued for underwriter			9,000,000
Subsequent Event | Over-Allotment Option | 6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Preferred stock to be issued by the option of underwriter	4,200,000
Expiration date	Aug. 25, 2017