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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Beginning Gross reserves			$ 329,888
Claims and claim expense payments for claims occurring during:
Ending Gross reserves	$ 341,784		341,784
Benefits, claims and settlement expenses	134,895	$ 135,710	444,870	$ 403,631
Property and Casualty segment
Segment Reporting Information [Line Items]
Beginning Gross reserves	329,831	320,961	307,757	301,569
Less: reinsurance recoverables	58,897	60,499	61,199	50,332
Net reserves, beginning of year	270,934	260,462	246,558	251,237
Incurred claims and claim expenses:
Claims occurring in the current period	115,393	116,709	386,945	351,270
Decrease in estimated reserves for claims occurring in prior years	(500)	(700)	(2,100)	(4,300)
Total claims and claim expenses incurred	114,893	116,009	384,845	346,970
Claims and claim expense payments for claims occurring during:
Current period	97,188	99,832	245,213	228,462
Prior periods	28,054	27,976	125,605	121,082
Total claims and claim expense payments	125,242	127,808	370,818	349,544
Net reserves, end of year	260,585	248,663	260,585	248,663
Plus: reinsurance recoverables	57,302	61,893	57,302	61,893
Ending Gross reserves	317,887	310,556	317,887	310,556
Life and Annuity segments
Claims and claim expense payments for claims occurring during:
Net reserves, end of year	23,897	22,231	23,897	22,231
Benefits, claims and settlement expenses	$ 20,002	$ 19,701	$ 60,025	$ 56,661