Offsetting Assets and Liabilities Offsetting Liabilities (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Derivative liabilities, fair value, gross liability		$ 6,922	$ 41,205
Derivative liabilities, fair value, gross amount offset in balance sheet		0	0
Derivative liabilities, fair value, amount not offset against collateral		6,922	41,205
Derivative liabilities, gross amount not offset in the balance sheet, financial instruments posted as collateral	[1]	(6,913)	(9,079)
Derivative liabilties, gross amount not offset in the balance sheet, cash posted as collateral	[1]	0	(32,111)
Derivative liabilities, fair value, net amount offset against collateral		9	15
Repurchase agreements, gross liability		2,898,952	2,589,420
Repurchase agreements, gross amount offset in balance sheet		0	0
Repurchase agreements, amount not offset against collateral		2,898,952	2,589,420
Repurchase agreements, gross amount not offset in balance sheet, financial instruments posted as collateral	[1]	(2,898,952)	(2,589,420)
Repurchase agreements, gross amount not offset in balance sheet, cash posted as collateral	[1]	0	0
Repurchase agreements, net amount offset against collateral		0	0
Total gross liabilities		2,905,874	2,630,625
Total gross liabilities, gross amount offset in balance sheet		0	0
Total liabilities, amount not offset against collateral		2,905,874	2,630,625
Total liabilities, gross amount not offset in balance sheet, financial instruments posted as collateral	[1]	(2,905,865)	(2,598,499)
Total liabilities, gross amount not offset in the balance sheet, cash posted as collateral	[1]	0	(32,111)
Total liabilities, net amount offset against collateral		$ 9	$ 15

[1] Amounts disclosed for collateral received by or posted to the same counterparty include cash and the fair value of MBS up to and not exceeding the net amount of the asset or liability presented in the balance sheet. The fair value of the actual collateral received by or posted to the same counterparty may exceed the amounts presented.