Other Comprehensive Income Other Comprehensive Income (Narrative) (Details) $ in Thousands	Jan. 01, 2018 USD ($)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of ASU No. 2016-01, net of taxes	$ (2,613,242)
Cumulative effect of adoption of ASU No 2018-02	401,539
Unrealized holding gains on available-for-sale securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of ASU No. 2016-01, net of taxes	(2,615,734)
Cumulative effect of adoption of ASU No 2018-02	$ 401,539