SCHEDULE VI-SUPPLEMENTARY INFORMATION CONCERNING PROPERTY-CASUALTY INSURANCE OPERATIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Claims and claim adjustment expenses incurred related to:
Current accident year	$ 488,700	$ 478,143	$ 440,452
Prior accident years	(75,284)	(49,950)	(38,868)
Amortization of deferred acquisition costs	288,697	267,738	252,515
Consolidated property-casualty insurance operations
SUPPLEMENTARY INFORMATION CONCERNING PROPERTY-CASUALTY INSURANCE OPERATIONS
Deferred policy acquisition costs	85,044	84,934	77,716
Claims and claim adjustment expense reserves	1,574,352	1,461,348	1,271,503
Unearned premiums, gross	540,213	496,505	451,449
Net premiums earned	839,111	791,366	737,937
Net investment income	68,870	62,085	54,876
Claims and claim adjustment expenses incurred related to:
Current accident year	488,700	478,143	440,452
Prior accident years	(75,284)	(49,950)	(38,868)
Amortization of deferred acquisition costs	288,697	267,738	252,515
Paid claims and claims adjustment expenses	319,930	301,356	283,185
Net premiums written	$ 860,337	$ 823,175	$ 749,854