Financial Instruments - Fair Values Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage-backed securities, at fair value	$ 18,247,789	[1]	$ 17,348,657	[1]
Investments in unconsolidated ventures, at fair value	44,030		44,403
Derivative assets, at fair value	70,190		262,059
Total, Assets	18,362,009		17,655,119
Derivatives, Liabilities	268,600		263,204
Total	268,600		263,204
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets, at fair value	596		2,591
Total, Assets	596		2,591
Derivatives, Liabilities	347
Total	347
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage-backed securities, at fair value	18,247,789	[1]	17,348,657	[1]
Derivative assets, at fair value	69,047		258,814
Total, Assets	18,316,836		17,607,471
Derivatives, Liabilities	268,253		263,204
Total	268,253		263,204
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in unconsolidated ventures, at fair value	44,030		44,403
Derivative assets, at fair value	547		654
Total, Assets	$ 44,577		$ 45,057

[1] For more detail about the fair value of the Company's MBS, refer to Note 4 - Mortgage-Backed Securities in these consolidated financial statements.