Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Notional Disclosures [Abstract]
Notional Amount	$ 14,991,653	$ 14,022,179
Fair Value
Asset	12,692	10,519
Collateral (held)/pledged	(2,525)	(2,685)
Net amount	10,167	7,834
(Liability)	(53,795)	(27,042)
Collateral (held)/pledged	225,404	132,129
Net amount	171,609	105,087
Designated as Hedging Instrument \| Fair value hedges: \| Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	5,099,293	4,955,686
Fair Value
Asset	4,339	7,163
(Liability)	$ (6,583)	$ (3,281)
Weighted- Average Pay Rate	2.42%	2.47%
Weighted- Average Receive Rate	1.54%	1.93%
Weighted- Average Remaining Term (in years)	11 years 7 months 20 days	11 years 3 months 3 days
Designated as Hedging Instrument \| Fair value hedges: \| Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 2,201,500	$ 1,413,200
Fair Value
Asset	1,303	76
(Liability)	$ (9,730)	$ (5,329)
Weighted- Average Pay Rate	1.66%	1.88%
Weighted- Average Receive Rate	2.06%	2.13%
Weighted- Average Remaining Term (in years)	2 years 2 months 19 days	1 year 3 months
Designated as Hedging Instrument \| Fair value hedges: \| Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount	$ 413,000	$ 524,000
Fair Value
Asset	4,954	476
(Liability)	$ (26)	$ (772)
Weighted- Average Pay Rate	1.36%	1.52%
Weighted- Average Receive Rate	1.95%	1.91%
Weighted- Average Remaining Term (in years)	3 years 4 months 17 days	2 years 9 months 29 days
Designated as Hedging Instrument \| Cash flow hedges: \| Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 458,000	$ 428,000
Fair Value
Asset	1,434	1,882
(Liability)	$ (11,391)	$ (1,514)
Weighted- Average Pay Rate	2.31%	2.36%
Weighted- Average Receive Rate	1.22%	2.12%
Weighted- Average Remaining Term (in years)	5 years 4 months 9 days	5 years 5 months 4 days
Not Designated as Hedging Instrument
Fair Value
Credit valuation adjustment	$ 0	$ 0
Credit valuation adjustment	117	63
Not Designated as Hedging Instrument \| Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	339,721	342,745
Fair Value
Asset	0	7
(Liability)	$ (22,683)	$ (14,046)
Weighted- Average Pay Rate	3.54%	3.55%
Weighted- Average Receive Rate	1.69%	2.00%
Weighted- Average Remaining Term (in years)	5 years 3 months 25 days	5 years 6 months 3 days
Not Designated as Hedging Instrument \| Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 3,111,639	$ 3,124,148
Fair Value
Asset	0	49
(Liability)	$ 0	$ (1,637)
Weighted- Average Pay Rate	1.17%	1.88%
Weighted- Average Receive Rate	1.39%	2.06%
Weighted- Average Remaining Term (in years)	1 year 3 days	1 year 7 months 28 days
Not Designated as Hedging Instrument \| Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount	$ 500,000	$ 525,000
Fair Value
Asset	604	79
(Liability)	$ 0	$ (80)
Weighted- Average Pay Rate	1.52%	1.64%
Weighted- Average Receive Rate	1.75%	1.68%
Weighted- Average Remaining Term (in years)	10 months 9 days	9 months 29 days
Not Designated as Hedging Instrument \| Basis swaps
Notional Disclosures [Abstract]
Notional Amount	$ 2,850,000	$ 2,670,000
Fair Value
Asset	58	787
(Liability)	$ (3,385)	$ (395)
Weighted- Average Pay Rate	1.49%	1.86%
Weighted- Average Receive Rate	0.66%	1.76%
Weighted- Average Remaining Term (in years)	10 months 28 days	10 months 24 days
Not Designated as Hedging Instrument \| Treasury futures
Notional Disclosures [Abstract]
Notional Amount	$ 18,500	$ 39,400
Fair Value
Asset		0
(Liability)	$ (114)	$ (51)
Weighted- Average Forward Price (in dollars per share)	$ 138.07	$ 128.29

Derivative, Weighted-Average Forward Price

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Fair value of securities received as collateral against derivative assets.

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Nominal or face amount used to calculate payments on the derivative asset.

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- Definition

Average fixed interest rate related to the group of interest rate derivatives.

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- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Average variable interest rate related to the group of interest rate derivatives.

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- Definition

Amount of credit risk valuation adjustment to derivative assets to properly reflect the credit quality of the counterparties.

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Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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