Organization and Significant Accounting Policies Organization and Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collateral of the fair value of domestic securities loaned (as a percentage)	102.00%
Collateral of the fair value of foreign securities loaned (as a percentage)	105.00%
Cash and Cash Equivalents [Abstract]
Bank overdrafts	$ 518,000	$ 12,850,000
Property, Plant and Equipment [Abstract]
Capitalized internal use software development costs, net of accumulated amortization	103,487,000	98,074,000
Capitalized internal use software development costs	34,164,000	30,420,000	$ 47,895,000
Life insurance and annuity future benefits with life contingencies	17,293,006,000	16,530,160,000
Annuity contract benefits liabilities without life contingencies	12,704,401,000	12,291,378,000
Business Combinations [Abstract]
Participating life and annuity policy benefit liabilities	$ 6,946,953,000	$ 6,844,640,000
Participating business of individual life insurance in-force (as a percentage)	10.00%	10.00%
Participating business of individual's life insurance premium income (as a percentage)	19.00%	18.00%	20.00%
Maximum
Property, Plant and Equipment [Abstract]
Finite-lived intangible asset, useful life	18 years
Life insurance and annuity future benefits with life contingencies	$ 4,500,000
Maximum | Software and Software Development Costs
Property, Plant and Equipment [Abstract]
Useful life	5 years
Minimum
Property, Plant and Equipment [Abstract]
Finite-lived intangible asset, useful life	2 years
Weighted Average
Property, Plant and Equipment [Abstract]
Finite-lived intangible asset, useful life	15 years