Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax asset:
Loss reserve discounting	$ 141,877	$ 136,100
Unearned premiums	134,971	120,246
Net operating losses	64,494	37,147
Other-than-temporary impairments	5,973	8,049
Employee compensation plans	60,551	60,552
Other	85,327	63,633
Gross deferred tax asset	493,193	425,727
Less valuation allowance	(79,488)	(33,250)
Deferred tax asset	413,705	392,477
Deferred tax liability:
Amortization of intangibles	12,761	12,832
Loss reserve discounting - transition rule	24,747	29,697
Deferred policy acquisition costs	113,084	103,947
Unrealized investment gains	100,241	93,330
Property, furniture and equipment	48,235	47,082
Investment funds	64,944	73,083
Other	62,809	50,212
Deferred tax liability	426,821	410,183
Net deferred tax liability	13,116	17,706
Operating Loss Carryforwards [Line Items]
Income taxes receivable	35,400
Current federal income taxes		13,400
Valuation allowance	79,500	$ 33,300
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, subject to expire	7,700
Operating loss carryforwards, not subject to expire	$ 305,400