Offsetting Assets and Liabilities - Offsetting of Derivative Liabilities (Detail) - USD ($)		Sep. 30, 2016	Dec. 31, 2015
Derivatives Liability
Gross Amounts of Recognized Liabilities	[1]	$ 382,321,000	$ 238,148,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	[1]	0	0
Net Amounts of Liabilities presented in the Condensed Consolidated Balance Sheets	[1]	382,321,000	238,148,000
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	[1],[2]	(151,820,000)	(117,240,000)
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Posted	[1]	(230,501,000)	(109,299,000)
Net Amount	[1]	0	11,609,000
Repurchase Agreements
Gross Amounts of Recognized Liabilities	[3]	12,060,502,000	12,126,048,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	[3]	0	0
Net Amounts of Liabilities presented in the Condensed Consolidated Balance Sheets	[3]	12,060,502,000	12,126,048,000
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	[2],[3]	(12,060,502,000)	(12,126,048,000)
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Posted	[3]	0	0
Net Amount	[3]	0	0
Secured Loans
Gross Amounts of Recognized Liabilities	[4]	1,650,000,000	1,650,000,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	[4]	0	0
Net Amounts of Liabilities presented in the Condensed Consolidated Balance Sheets	[4]	1,650,000,000	1,650,000,000
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	[2],[4]	(1,650,000,000)	(1,650,000,000)
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Posted	[4]	0	0
Net Amount	[4]	0	0
Total Borrowings
Gross Amounts of Recognized Liabilities		14,092,823,000	14,014,196,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets		0	0
Net Amounts of Liabilities presented in the Condensed Consolidated Balance Sheets		14,092,823,000	14,014,196,000
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	[2]	(13,862,322,000)	(13,893,288,000)
Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Posted		(230,501,000)	(109,299,000)
Net Amount		0	11,609,000
Fair value of securities pledged under reverse repurchase agreement		74,800,000
Fair value of securities pledged under repurchase agreement	[5]	13,344,339,000	13,460,288,000
Cash collateral posted by Company's derivative counterparties			4,900,000
Due from counterparties		241,200,000	109,300,000
Collateral pledged against secured loans		$ 2,000,000,000	1,900,000,000
Cash collateral posted			$ 0

[1] ash collateral was posted by the Company's derivative counterparties at September 30, 2016 (December 31, 2015: $4.9 million). Cash collateral posted by the Company on its derivatives was $241.2 million and $109.3 million at September 30, 2016 and December 31, 2015, respectively.

[2] Amounts represent collateral pledged that is available to be offset against liability balances associated with repurchase agreements, secured loans and derivatives.

[3] The fair value of securities pledged against the Company's borrowing under repurchase agreements was $13.3 billion and $13.5 billion at September 30, 2016 and December 31, 2015, respectively.

[4] The fair value of securities pledged against IAS Services LLC's borrowing under secured loans was $2.0 billion and $1.9 billion at September 30, 2016 and December 31, 2015, respectively.

[5] Amount pledged as collateral is measured at fair value as described in Note 2 - "Summary of Significant Accounting Policies." As of September 30, 2016, the Company also pledged Agency RMBS with a fair value of $169.8 million (December 31, 2015: $143.9 million) as collateral against its interest rate swaps. See Note 8 - "Derivative and Hedging Activities" for additional information.