Derivative Instruments Derivative Instruments (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		$ 147,850	$ 105,674
Derivative Asset, Amount Offset by Liabiilty		0	0
Derivative Assets	[1]	147,850	105,674
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		20,370	10,219
Derivative Liability, Amount Offset by Asset		0	0
Derivative Liabilities	[1]	20,370	10,219
Derivative Subject to Master Netting Agreement [Member]
Derivative Asset, Fair Value, Gross Asset		144,440	105,147
Derivative Asset, Amount Offset by Liabiilty		0	0
Derivative Asset, Net Amount Presented in the Balance Sheet		144,440	105,147
Derivative Asset, Not Offset, Policy Election Deduction		(9,933)	(8,104)
derivatve asset, fair value of collateral		(37,441)	(59,525)
Derivative Asset, Fair Value, Amount Offset Against Collateral		97,066	37,518
Derivative Liability, Fair Value, Gross Liability		19,915	10,083
Derivative Liability, Amount Offset by Asset		0	0
Derivative Liability, Net Amount Presented in the Balance Sheet		19,915	10,083
Derivative Liability, Not Offset, Policy Election Deduction		(9,933)	(8,104)
Derivative Liability, Fair Value of Collateral		(8,719)	(437)
Derivative Liability, Fair Value, Amount Offset Against Collateral		1,263	1,542
Derivative Not Subject to Master Netting Agreement [Member]
Derivative Asset, Fair Value, Gross Asset		3,410	527
Derivative Asset, Amount Offset by Liabiilty		0	0
Derivative Asset, Not Subject to Master Netting Arrangement		3,410	527
Derivative Liability, Fair Value, Gross Liability		455	136
Derivative Liability, Amount Offset by Asset		0	0
Derivative Liability, Not Subject to Master Netting Arrangement		$ 455	$ 136

[1] * The fair value of each class of derivative is shown in Note 11.