Business Combination (Schedule of Recognized Identified Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	May 05, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Business Acquisition [Line Items]
Gain on bargain purchase		$ (74,408)	$ 0	$ (74,408)	$ 0
NORCAL Group
Business Acquisition [Line Items]
Fixed maturities, available for sale	$ 1,100,058
Equity investments, available for sale	374,484
Short-term investments	61,289
Business owned life insurance	12,581
Investment in unconsolidated subsidiaries	26,948
Other investments	32,461
Cash and cash equivalents	28,233
Premiums receivable	110,905
Receivable from reinsurers on paid losses and loss adjustment expenses	266
Receivable from reinsurers on unpaid losses and loss adjustment expenses	93,342
Prepaid reinsurance premiums	9,238
Deferred tax asset, net	46,759
Operating lease ROU assets	4,385
Intangible assets	14,000
Other assets	38,648
Reserve for losses and loss adjustment expenses	(1,182,445)
Unearned premiums	(178,400)
Reinsurance premiums payable	(12,981)
Operating lease liabilities	(5,275)
Other liabilities	(51,279)
Total identifiable net assets acquired	523,217
Gain on bargain purchase	(74,408)
Total acquisition consideration	$ 448,809