Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Deferred tax asset:
Loss reserve discounting	$ 136,100	$ 130,513	$ 40,000
Unearned premiums	120,246	112,190
Net operating losses	37,147	37,463
Other-than-temporary impairments	8,049	9,910
Employee compensation plans	60,552	56,027
Other	63,633	58,809
Gross deferred tax asset	425,727	404,912
Less valuation allowance	(33,250)	(35,195)
Deferred tax asset	392,477	369,717
Deferred tax liability:
Amortization of intangibles	12,832	13,641
Loss reserve discounting - transition rule	29,697	41,088
Deferred policy acquisition costs	103,947	99,293
Unrealized investment gains	93,330	35,430
Property, furniture and equipment	47,082	39,239
Investment funds	73,083	51,712
Other	50,212	53,824
Deferred tax liability	410,183	334,227
Net deferred tax liability (asset)	17,706
Net deferred tax liability (asset)		(35,490)
Operating Loss Carryforwards [Line Items]
Current federal and foreign income taxes	13,398	703
Current federal income taxes		700
Valuation allowance	33,300	$ 35,200
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, subject to expire	9,000
Operating loss carryforwards, not subject to expire	$ 169,000