Organization and Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended		21 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Description of management fee			The Manager is supervised and directed by our board of directors and is responsible for (i) the selection, purchase and sale of our investment portfolio; (ii) our financing and hedging activities; and (iii) providing us with management services. The Manager will also perform such other services and activities relating to our assets and operations as may be appropriate. In exchange for these services, the Manager receives a management fee paid monthly in arrears in an amount equal to one-twelfth of 1.20% of our Equity (as defined in the Management Agreement).
Monthly management fee payment in arrears, one-twelfth of percentage of equity			1.20%
MBS initial fixed interest rate required, period	Three to ten years		Three to ten years
Options to purchase common stock not included in the computation of diluted EPS	5,000	494,700
Minimum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
MBS initial fixed interest rate required, period	3 years		3 years
Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
MBS initial fixed interest rate required, period	10 years		10 years
Non-Agency MBS included with the Agency MBS	$ 70		$ 70
Derivative, fixed rate obligation period	10 years