Fair Value Measurements - Valuation of Financial Instruments that are Marked-to-Market on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets
Mortgage-backed securities	$ 203,597	$ 195,391
Derivative instruments	37,802	6,036
Liabilities
Derivative instruments	(38,045)	(21,219)
Fair Value Measurements Recurring
Assets
Mortgage-backed securities	203,597	195,391
Derivative instruments	52,007	15,314
Total earning assets	255,604	210,705
Liabilities
Derivative instruments	(52,250)	(30,497)
Fair Value Measurements Recurring \| Level 1
Assets
Mortgage-backed securities	0	0
Derivative instruments	0	0
Total earning assets	0	0
Liabilities
Derivative instruments	0	0
Fair Value Measurements Recurring \| Level 2
Assets
Mortgage-backed securities	203,597	195,391
Derivative instruments	52,007	15,314
Total earning assets	255,604	210,705
Liabilities
Derivative instruments	(52,250)	(30,497)
Fair Value Measurements Recurring \| Level 3
Assets
Mortgage-backed securities	0	0
Derivative instruments	0	0
Total earning assets	0	0
Liabilities
Derivative instruments	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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