Segment Information - Additional Significant Financial Information by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
DAC amortization expense	$ 109,889	$ 102,185	$ 96,732
Income tax expense (benefit)	1,194	(80,772)	30,467
Property and Casualty
Segment Reporting Information [Line Items]
DAC amortization expense	79,073	76,967	74,950
Retirement
Segment Reporting Information [Line Items]
DAC amortization expense	23,186	17,759	14,635
Life
Segment Reporting Information [Line Items]
DAC amortization expense	7,630	7,459	7,147
Operating Segments | Property and Casualty
Segment Reporting Information [Line Items]
Income tax expense (benefit)	(6,622)	(3,279)	4,627
Operating Segments | Retirement
Segment Reporting Information [Line Items]
Income tax expense (benefit)	10,000	(19,498)	20,334
Operating Segments | Life
Segment Reporting Information [Line Items]
Income tax expense (benefit)	4,979	(51,876)	9,775
Corporate and Other | Corporate and Other
Segment Reporting Information [Line Items]
Income tax expense (benefit)	$ (7,163)	$ (6,119)	$ (4,269)