Repurchase Agreements Offsetting (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Offsetting Liabilities [Line Items]
Gross Amount of Recognized Liabilities		$ 4,252,893	$ 3,267,984
Gross Amount Offset in the Balance Sheet		0	0
Net Amount of Liabilities Presented in the Balance Sheet		4,252,893	3,267,984
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	[1]	(4,252,893)	(3,267,984)
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 repurchase agreement 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.