Property and Casualty Unpaid Claims and Claim Expenses - Summary of Reinsurance Reserve Balances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Beginning Gross reserves			$ 347,749
Claims and claim expense payments for claims occurring during:
Ending Gross reserves	$ 384,636		384,636
Benefits, claims and settlement expenses	161,846	$ 134,895	473,686	$ 444,870
Property and Casualty
Segment Reporting Information [Line Items]
Beginning Gross reserves	352,817	329,831	319,182	307,757
Less: reinsurance recoverables	62,883	58,897	57,409	61,199
Net reserves, beginning of year	289,934	270,934	261,773	246,558
Incurred claims and claim expenses:
Claims occurring in the current period	140,035	115,393	408,028	386,945
Decrease in estimated reserves for claims occurring in prior years	0	(500)	(300)	(2,100)
Total claims and claim expenses incurred	140,035	114,893	407,728	384,845
Claims and claim expense payments for claims occurring during:
Current period	106,187	97,188	233,638	245,213
Prior periods	28,997	28,054	141,078	125,605
Total claims and claim expense payments	135,184	125,242	374,716	370,818
Net reserves, end of year	294,785	260,585	294,785	260,585
Plus: reinsurance recoverables	63,262	57,302	63,262	57,302
Ending Gross reserves	358,047	317,887	358,047	317,887
Life and Annuity segments
Claims and claim expense payments for claims occurring during:
Net reserves, end of year	26,589	23,897	26,589	23,897
Benefits, claims and settlement expenses	$ 21,811	$ 20,002	$ 65,958	$ 60,025