Summary of the Significant Accounting Policies - Narrative (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	[1]
Summary Of Significant Accounting Policies [Line Items]
Non-Agency RMBS, at fair value	$ 3,330,063,000				$ 3,675,841,000				$ 3,330,063,000		$ 3,675,841,000
Agency RMBS, at fair value	4,167,754,000				6,514,824,000				4,167,754,000		6,514,824,000
Interest income	260,823,000	$ 250,953,000	$ 221,096,000	$ 201,194,000	201,912,000	$ 211,876,000	$ 215,804,000	$ 243,145,000	934,068,000	[1]	872,737,000	[1]	$ 687,795,000
Accrual for income tax penalties and interest	0				0				0		0
Interest-Only RMBS
Summary Of Significant Accounting Policies [Line Items]
Non-Agency RMBS, at fair value	266,000,000				245,000,000				266,000,000		245,000,000
Agency RMBS, at fair value	145,000,000				273,000,000				145,000,000		273,000,000
Non-Agency RMBS, Fair Value Option
Summary Of Significant Accounting Policies [Line Items]
Non-Agency RMBS, at fair value	19,000,000				20,000,000				19,000,000		20,000,000
Other Assets
Summary Of Significant Accounting Policies [Line Items]
Total REO assets	$ 13,000,000				$ 18,000,000				13,000,000		18,000,000
Residential Mortgage-Backed Securities | Interest-Only RMBS
Summary Of Significant Accounting Policies [Line Items]
Interest income									$ 43,000,000		$ 49,000,000

[1] Includes interest income of consolidated VIEs of $678,623, $575,715, and $428,992 for the years ended December 31, 2016, 2015, and 2014 respectively. See Note 8 to consolidated financial statements for further discussion.