Basis of Presentation - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)	$ (15,041)	$ 0
Future lease commitments			$ 9,093
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)	(15,041)
Stranded Tax Amounts Reclassified	50,034
Benefit Plans
Basis of Presentation [Line Items]
Cumulative effect of change in accounting principle (3)	0
Stranded Tax Amounts Reclassified	$ (2,134)