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Statements of Cash Flows (Cash Flow Supplemental Disclosures) (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020
Interest		$ 14,547	$ 14,920
Federal income tax		66,000	0
Operating cash flows from operating leases		4,348	4,443
Operating cash flows from financing leases		4	10
Financing cash flows from finance leases		229	314
Assets acquired under finance lease arrangements		183	119
Assets acquired under operating lease arrangements		16	4,358
Non-cash purchase of property and equipment		35	60
Available-for-sale Securities
Corporate actions related to securities	[1]	45,392	18,224
Equity Securities [Member]
Corporate actions related to securities	[1]	527	890
Held-to-maturity Securities [Member]
Corporate actions related to securities	[1]	$ 0	$ 2,596
[1] Examples of corporate actions include exchanges, non-cash acquisitions, and stock splits.

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Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

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