Repurchase Agreements Offsetting (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Gross Amount of Recognized Liabilities		$ 2,690,858	$ 2,565,902
Gross Amount Offset in the Balance Sheet		0	0
Net Amount of Liabilities Presented in the Balance Sheet		2,690,858	2,565,902
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	[1]	(2,690,858)	(2,565,902)
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash		0	0
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral		$ 0	$ 0

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