Note 9 - Other Assets - Components of Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Other Assets [Abstract]
Prepaid federal income taxes (Note 10)	$ 191,889	$ 134,800
Company-owned life insurance	112,311	105,721
Reinsurance recoverables	66,515	16,976
Internal-use software (net of accumulated amortization of $80,060 and $73,498)	61,549	58,356
Loaned securities (Note 5)	57,922	66,442
Accrued investment income	36,093	32,333
Right-of-use assets	34,662	37,866
Property and equipment (net of accumulated depreciation of $70,519 and $68,436)	27,168	29,523
Deferred policy acquisition costs	17,926	20,759
Unbilled receivables	8,581	13,772
Assets held for sale	0	24,908
Other Assets, Miscellaneous	26,214	26,163
Other Assets	640,830	567,619
Accumulated amortization	80,060	73,498
Accumulated depreciation	$ 70,519	$ 68,436