Summary of Significant Accounting Policies - Deferred Policy Acquisition Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	$ 276,668	$ 298,742
Property and Casualty
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	28,616	30,033
Supplemental
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	1,967
Retirement (annuity)
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	185,294	209,231
Life
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	$ 60,791	$ 59,478