Fair Value of Financial Instruments (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
Assets:
Agency MBS	$ 6,549,451,000		$ 6,519,221,000
Securities obtained and pledged as collateral	446,375,000		383,743,000
Linked Transactions	106,859,000		28,181,000
Swaps	2,755,000		13,000,000
Liabilities:
Swaps	57,426,000	[1]	28,217,000	[1]
Obligation to return securities obtained as collateral	446,375,000		383,743,000
Level 2
Components of financial instruments carried at fair value
Credit valuation adjustment to derivative liabilities	0
Credit valuation adjustment to derivative assets	0
Recurring basis | Level 1
Assets:
Agency MBS	0
Non-Agency MBS, including MBS transferred to consolidated VIEs	0
Securities obtained and pledged as collateral	446,375,000
Linked Transactions	0
Swaps	0
Total assets carried at fair value	446,375,000
Liabilities:
Swaps	0
Obligation to return securities obtained as collateral	446,375,000
Total liabilities carried at fair value	446,375,000
Recurring basis | Level 2
Assets:
Agency MBS	6,549,451,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	5,001,337,000
Securities obtained and pledged as collateral	0
Linked Transactions	106,859,000
Swaps	2,755,000
Total assets carried at fair value	11,660,402,000
Liabilities:
Swaps	57,426,000
Obligation to return securities obtained as collateral	0
Total liabilities carried at fair value	57,426,000
Recurring basis | Level 3
Assets:
Agency MBS	0
Non-Agency MBS, including MBS transferred to consolidated VIEs	0
Securities obtained and pledged as collateral	0
Linked Transactions	0
Swaps	0
Total assets carried at fair value	0
Liabilities:
Swaps	0
Obligation to return securities obtained as collateral	0
Total liabilities carried at fair value	0
Recurring basis | Estimated Fair Value
Assets:
Agency MBS	6,549,451,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	5,001,337,000
Securities obtained and pledged as collateral	446,375,000
Linked Transactions	106,859,000
Swaps	2,755,000
Total assets carried at fair value	12,106,777,000
Liabilities:
Swaps	57,426,000
Obligation to return securities obtained as collateral	446,375,000
Total liabilities carried at fair value	$ 503,801,000

[1] The fair value of securities pledged against the Company’s Swaps was $75.1 million and $73.9 million at June 30, 2014 and December 31, 2013, respectively.