Summary of Significant Accounting Policies - Deferred Policy Acquisition Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total	$ 257,826	$ 267,580
Retirement (annuity)
Segment Reporting Information [Line Items]
Total	174,661	188,117
Life
Segment Reporting Information [Line Items]
Total	53,974	51,859
Property and Casualty
Segment Reporting Information [Line Items]
Total	$ 29,191	$ 27,604