Property and Casualty Unpaid Claims and Claim Expenses - Summary of Reinsurance Reserve Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017
Segment Reporting Information [Line Items]
Beginning Gross reserves	$ 347,749
Claims and claim expense payments for claims occurring during:
Ending Gross reserves	358,317
Benefits, claims and settlement expenses	143,562		$ 144,096
Property and Casualty
Segment Reporting Information [Line Items]
Beginning Gross reserves	319,182		307,757
Less: reinsurance recoverables	57,409		61,199
Net reserves, beginning of year	261,773		246,558
Incurred claims and claim expenses:
Claims occurring in the current period	120,988		123,204
Decrease in estimated reserves for claims occurring in prior years	(300)		(1,000)
Total claims and claim expenses incurred	120,688		122,204
Claims and claim expense payments for claims occurring during:
Current period	47,048		52,380
Prior periods	67,075		62,013
Total claims and claim expense payments	114,123		114,393
Net reserves, end of year	268,338		254,369
Plus: reinsurance recoverables	62,917		61,804
Ending Gross reserves	331,255		316,173
Life and Annuity segments
Claims and claim expense payments for claims occurring during:
Net reserves, end of year	27,062		$ 23,860
Benefits, claims and settlement expenses	$ 21,892	$ 22,874