Property and Casualty Unpaid Claims and Claim Expenses - Summary of Reinsurance Reserve Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Gross reserves, beginning of year	$ 329,888
Less: reinsurance recoverables	70,474
Claims and claim expense payments for claims occurring during:
Plus: reinsurance recoverables	68,446	$ 70,474
Gross reserves, end of year	347,749	329,888
Benefits, claims and settlement expenses, Net Amount	582,306	541,004	$ 496,364
Property and Casualty segment
Segment Reporting Information [Line Items]
Gross reserves, beginning of year	307,757	301,569	311,097
Less: reinsurance recoverables	61,199	50,332	43,740
Net reserves, beginning of year	246,558	251,237	267,357
Incurred claims and claim expenses:
Claims occurring in the current year	498,989	471,099	432,811
Decrease in estimated reserves for claims occurring in prior years	2,700	7,000	12,500
Total claims and claim expenses incurred	496,289	464,099	420,311
Claims and claim expense payments for claims occurring during:
Current year	333,385	323,025	294,449
Prior years	147,689	145,753	141,982
Total claims and claim expense payments	481,074	468,778	436,431
Net reserves, end of year	261,773	246,558	251,237
Plus: reinsurance recoverables	57,409	61,199	50,332
Gross reserves, end of year	319,182	307,757	301,569
Life and Annuity segments
Segment Reporting Information [Line Items]
Net reserves, beginning of year	22,131	22,151
Claims and claim expense payments for claims occurring during:
Net reserves, end of year	28,567	22,131	22,151
Benefits, claims and settlement expenses, Net Amount	$ 86,017	$ 76,905	$ 76,053