Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		$ 0
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	$ 5,974,000	6,117,000	$ 5,974,000	$ 6,117,000	$ 5,848,000	$ 6,207,000	$ 7,080,000	$ 6,930,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(40,000)	345,000	161,000	698,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	246,000	(213,000)	(152,000)	(241,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(80,000)	(467,000)	(242,000)	(643,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			160,000	639,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		(627,000)		(627,000)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(41,000)	332,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	246,000		(152,000)
Fair Value, Inputs, Level 3 [Member] | Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	75,000	79,000	75,000	79,000	66,000	72,000	74,000	72,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000	1,000	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	9,000	5,000	3,000	7,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0	(1,000)	(1,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0		0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	9,000		3,000
Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,000	3,000	2,000	3,000	2,000	3,000	4,000	5,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0	(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0	0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(1,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0		0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000		66,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			23,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies				0
Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000	66,000	62,000	46,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000	24,000	30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)	(5,000)	3,000
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			23,000	30,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	12,000
Interest Rate Swap [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	86,000		86,000			67,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			24,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			(5,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			24,000
Credit Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	(1,000)		(1,000)			$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings			(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements			0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held			(1,000)
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability								46,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				30,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				30,000
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	85,000	73,000	85,000	73,000	86,000		62,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	12,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies		0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	1,000	12,000
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0		0
Credit Derivative [Member] | Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability		0		0				(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				1,000
Credit Derivative [Member] | Credit Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	(1,000)	0	(1,000)	0	(1,000)		(1,000)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	1,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Interest Rate Swap [Member] | Derivative [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability		73,000		73,000				$ 47,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings				29,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements				(3,000)
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held				29,000
Interest Rate Swap [Member] | Interest Rate Swap [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	86,000	73,000	$ 86,000	$ 73,000	$ 87,000		$ 63,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	1,000	11,000
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2,000)	(1,000)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 1,000	$ 11,000