Stockholders' Equity AOCI table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income		$ 354,764		$ 91,318
Reclassification related to the Tax Act						$ 0
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, Net of Tax		264,751		(188,504)		88,670
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Net of Tax, Attributable to Parent		389,655		(94,392)		274,507
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	[1]	363,020		96,921		295,169		$ 156,963
Reclassification related to the Tax Act	[1],[2]					49,657
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, Net of Tax	[1]	265,910		(191,158)		88,534
Accumulated Other-than-Temporary Impairment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income		1,974		3,133		537		311
Reclassification related to the Tax Act	[2]					90
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, Net of Tax		(1,159)		2,654		136
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	[3]	(10,230)		(8,736)		(10,723)		(7,719)
Reclassification related to the Tax Act	[2],[3]					(1,521)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Reclassification Adjustment, Net of Tax	[3]	0		0		0
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income		354,764		91,318		284,983		$ 149,555
Reclassification related to the Tax Act	[2]					48,226
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Net of Tax, Attributable to Parent		(1,305)		319		(1,468)
reclassifications out of accumulated other comprehensive income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Net of Tax, Attributable to Parent		(1,305)		319		1,468
reclassifications out of accumulated other comprehensive income | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	[1]	189		(1,610)		15
reclassifications out of accumulated other comprehensive income | Accumulated Other-than-Temporary Impairment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax		0	[1]	(58)	[1]	0	[4]
reclassifications out of accumulated other comprehensive income | Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Gain (Loss), Reclassification Adjustment from AOCI, Net of Tax	[5]	$ (1,494)		1,987		$ (1,483)
Accounting Standards Update 2016-01 | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	[1],[6]			(5,480)
Accounting Standards Update 2016-01 | AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	[6]			$ (5,480)

[1] See Note 2 for further information.

[2] Reclassification of the initial impact of the remeasurement of deferred tax assets and liabilities upon enactment of the Tax Act. See discussion of this accounting change as discussed in Note 1.

[3] For descriptions of the underfunded portion of our postretirement benefit plans, see Note 8 - Other Retirement Plans, and for certain other defined benefit plans, see Note 8 - Defined Benefit Pension Plans.

[4] Unrealized net investment gains (losses) relate to available-for-sale securities and include the impact of taxes, deferred acquisition costs, value of insurance in force acquired, unearned revenue reserves and policyholder liabilities. See Note 2 for further information.

[5] For descriptions of the underfunded portion of our postretirement benefit plans, see Note 8 - Other Retirement Plans, and for certain other defined benefit plans, see Note 8 - Defined Benefit Plans.

[6] See Note 1 to our consolidated financial statements for further discussion on this one-time adjustment related to an accounting change.