Offsetting Assets and Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) counterparty	Dec. 31, 2016 USD ($)
Swaps, at fair value
Gross Amounts of Recognized Assets	$ 119	$ 233
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	119	233
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	(119)	(233)
Cash Collateral Received	0	0
Net Amount	0	0
Swaps, at fair value
Gross Amounts of Recognized Liabilities	0	46,954
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	0	46,954
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	0	0
Cash Collateral Pledged	0	(46,954)
Net Amount	0	0
Repurchase agreements and other advances
Gross Amounts of Recognized Liabilities	8,137,543	8,687,478
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	8,137,543	8,687,478
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	(8,131,319)	(8,682,864)
Cash Collateral Pledged	(6,224)	(4,614)
Net Amount	0	0
Total
Gross Amounts of Recognized Liabilities	8,137,543	8,734,432
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	8,137,543	8,734,432
Gross Amounts Not Offset in the Consolidated Balance Sheet
Financial Instruments	(8,131,319)	(8,682,864)
Cash Collateral Pledged	(6,224)	(51,568)
Net Amount	0	0
Additional disclosures
Excess collateral	4,800	6,900
Fair value of securities pledged against the swaps	31,100	32,500
Fair value of financial instruments pledged against the repurchase agreements and other advances	9,900,000	10,500,000
Unamortized debt issuance expense	$ 441	210
Number of repurchase agreement counterparties with unconditional right of setoff | counterparty	1
Swaps, at fair value
Swaps, at fair value
Gross Amounts of Recognized Assets	$ 119	233
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	119	233
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	(119)	(233)
Cash Collateral Received	0	0
Net Amount	$ 0	$ 0