Fair Values Level 3 Financial Instruments Changes in Fair Value (Details) - Fair Value, Measurements, Recurring - Fair Value, Inputs, Level 3 - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset Balance, beginning of period		$ 100,414	$ 189,312
Purchases		24,834	79,726
Disposals		(3,499)	(10,211)
Realized and unrealized gains (losses), net, included in net income		0	0
Realized and unrealized gains (losses), net, included in other comprehensive income		191	3,740
Transfers Into Level 3		0	7,082
Transfers out of Level 3	[1]	(70,918)	(97,293)
Amortization included in net income		(16)	256
Asset Balance, end of period		51,006	165,132
Corporate Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset Balance, beginning of period		22,011	33,600
Purchases		6,000	0
Disposals		(2,673)	(7,682)
Realized and unrealized gains (losses), net, included in net income		0	0
Realized and unrealized gains (losses), net, included in other comprehensive income		376	812
Transfers Into Level 3		0	7,082
Transfers out of Level 3		(6,000)	(2,000)
Amortization included in net income		(16)	282
Asset Balance, end of period		19,698	30,470
Residential mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset Balance, beginning of period		0	9,124
Purchases		2,124	23,940
Disposals		0	0
Realized and unrealized gains (losses), net, included in net income		0	0
Realized and unrealized gains (losses), net, included in other comprehensive income		0	0
Transfers Into Level 3		0	0
Transfers out of Level 3		0	(9,124)
Amortization included in net income		0	0
Asset Balance, end of period		2,124	23,940
Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset Balance, beginning of period		67,940	85,701
Purchases		0	35,531
Disposals		(186)	(423)
Realized and unrealized gains (losses), net, included in net income		0	0
Realized and unrealized gains (losses), net, included in other comprehensive income		498	2,590
Transfers Into Level 3		0	0
Transfers out of Level 3		(59,918)	(30,826)
Amortization included in net income		0	(26)
Asset Balance, end of period		8,334	87,367
Other asset backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset Balance, beginning of period		3,601	53,480
Purchases		16,710	20,255
Disposals		(640)	(2,106)
Realized and unrealized gains (losses), net, included in net income		0	0
Realized and unrealized gains (losses), net, included in other comprehensive income		(869)	(13)
Transfers Into Level 3		0	0
Transfers out of Level 3		(5,000)	(55,343)
Amortization included in net income		0	0
Asset Balance, end of period		13,802	16,299
Non-redeemable preferred stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset Balance, beginning of period		6,862	7,407
Purchases		0	0
Disposals		0	0
Realized and unrealized gains (losses), net, included in net income		0	0
Realized and unrealized gains (losses), net, included in other comprehensive income		186	(351)
Transfers Into Level 3		0	0
Transfers out of Level 3		0	0
Amortization included in net income		0	0
Asset Balance, end of period		7,048	7,056
Index Product Embedded Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liability balance, beginning of period		40,028	27,774
Purchases		6,899	5,226
Settlements		(3,364)	(2,476)
Realized and unrealized gains (losses), net, included in net income		15,812	(2,445)
Realized and unrealized gains (losses), net, included in other comprehensive income		0	0
Transfers Into Level 3		0	0
Transfers out of Level 3	[1]	0	0
Liability balance, end of period		$ 59,375	$ 32,969

[1] Transfers out of Level 3 include those assets that we are now able to obtain pricing from a third-party pricing vendor that uses observable inputs. The fair values of newly issued securities often require additional estimation until a market is created, which is generally within a few months after issuance. Once a market is created, as was the case for the majority of the security transfers out of the Level 3 category above, Level 2 valuation sources become available. There were no transfers between Level 1 and Level 2 during the periods presented above.