Goodwill and Other Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 137,683,000	$ 137,683,000
Amortization expense included in general insurance expenses	3,002,000	3,732,000	$ 4,096,000
Intangible assets with indefinite lives	0
2018	1,800,000
2019	1,800,000
2020	1,800,000
2021	1,800,000
2022	1,800,000
Empower Retirement Segment
Goodwill [Line Items]
Goodwill	$ 137,683,000	$ 137,683,000