Property and Casualty Unpaid Claims and Claim Expenses - Summary of Reinsurance Reserve Balances (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Beginning Gross reserves				$ 347,749
Claims and claim expense payments for claims occurring during:
Ending Gross reserves	$ 379,833			379,833
Benefits, claims and settlement expenses	168,278	$ 165,879		311,840	$ 309,975
Property and Casualty
Segment Reporting Information [Line Items]
Beginning Gross reserves	331,255	316,173	$ 307,757	319,182	307,757
Less: reinsurance recoverables	62,917	61,804	61,199	57,409	61,199
Net reserves, beginning of year	268,338	254,369	246,558	261,773	246,558
Incurred claims and claim expenses:
Claims occurring in the current period	147,005	148,348		267,993	271,552
Decrease in estimated reserves for claims occurring in prior years	0	(600)		(300)	(1,600)
Total claims and claim expenses incurred	147,005	147,748		267,693	269,952
Claims and claim expense payments for claims occurring during:
Current period	80,403	95,645		127,451	148,025
Prior periods	45,006	35,538		112,081	97,551
Total claims and claim expense payments	125,409	131,183		239,532	245,576
Net reserves, end of year	289,934	270,934	254,369	289,934	270,934
Plus: reinsurance recoverables	62,883	58,897	61,804	62,883	58,897
Ending Gross reserves	352,817	329,831	316,173	352,817	329,831
Life and Annuity segments
Claims and claim expense payments for claims occurring during:
Net reserves, end of year	27,016	$ 22,682		27,016	22,682
Benefits, claims and settlement expenses	$ 21,273		$ 18,131	$ 44,147	$ 40,023