Basis of Presentation - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)	$ 0	$ 0	$ (15,041)	$ 0
Future lease commitments	8,416		8,416
Retained earnings
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)			15,041	0
Accumulated other comprehensive income, net of tax:
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)			(15,041)	$ 0
Stranded Tax Amounts Reclassified			47,900
Net Unrealized Investment Gains and Losses on Fixed Maturity and Equity Securities
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)	0		(15,041)
Stranded Tax Amounts Reclassified			50,034
Benefit Plans
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)	$ 0		0
Stranded Tax Amounts Reclassified			$ (2,134)