Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Notional Disclosures [Abstract]
Notional Amount	$ 13,186,456		$ 9,955,745
Fair Value
Asset	7,560		7,487
Collateral (held)/pledged	(4,425)		(1,778)
Net amount	3,135		5,709
(Liability)	(27,429)		(19,633)
Collateral (held)/pledged	100,830		47,018
Net amount	73,401		27,385
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	4,708,809		3,097,084
Fair Value
Asset	3,481		3,004
(Liability)	$ (5,531)		$ (4,326)
Weighted- Average Pay Rate	2.52%		2.42%
Weighted- Average Receive Rate	2.52%		2.58%
Weighted- Average Remaining Term (in years)	11 years 14 days	9 years 9 months
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Swap, Receive Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 1,822,200		$ 1,871,200
Fair Value
Asset	518		547
(Liability)	$ (5,017)		$ (4,484)
Weighted- Average Pay Rate	2.47%		2.50%
Weighted- Average Receive Rate	2.02%		1.84%
Weighted- Average Remaining Term (in years)	1 year 4 months 28 days	1 year 6 months 29 days
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Swap, Receive Fixed Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 300,000		$ 160,000
Fair Value
Asset	1,250		338
(Liability)	$ 0		$ (28)
Weighted- Average Pay Rate	2.41%		2.35%
Weighted- Average Receive Rate	2.76%		3.06%
Weighted- Average Remaining Term (in years)	2 years 2 months 8 days	2 years 10 months 28 days
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 373,000		$ 373,000
Fair Value
Asset	887		2,441
(Liability)	$ (1,100)		$ (99)
Weighted- Average Pay Rate	2.40%		2.40%
Weighted- Average Receive Rate	2.81%		2.83%
Weighted- Average Remaining Term (in years)	5 years 7 months 13 days	6 years 1 month 13 days
Not Designated as Hedging Instrument [Member]
Fair Value
Credit valuation adjustment	$ (2)		$ (60)
Credit valuation adjustment	38		21
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	319,252		316,664
Fair Value
Asset	0		796
(Liability)	$ (15,469)		$ (10,399)
Weighted- Average Pay Rate	3.69%		3.69%
Weighted- Average Receive Rate	2.57%		2.52%
Weighted- Average Remaining Term (in years)	5 years 9 months 29 days	6 years 3 months
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap, Receive Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 2,758,595		$ 2,347,371
Fair Value
Asset	0		0
(Liability)	$ 0		$ 0
Weighted- Average Pay Rate	2.43%		2.37%
Weighted- Average Receive Rate	2.38%		2.10%
Weighted- Average Remaining Term (in years)	1 year 21 days	10 months 9 days
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap, Receive Fixed Callable [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 330,000
Fair Value
Asset	294
(Liability)	$ 0
Weighted- Average Pay Rate	2.39%
Weighted- Average Receive Rate	2.48%
Weighted- Average Remaining Term (in years)	9 months 29 days
Not Designated as Hedging Instrument [Member] \| Basis Swap [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 2,545,500		$ 1,770,026
Fair Value
Asset	1,132		421
(Liability)	$ (162)		$ (130)
Weighted- Average Pay Rate	2.27%		2.45%
Weighted- Average Receive Rate	2.35%		2.49%
Weighted- Average Remaining Term (in years)	1 year 25 days	1 year 3 months 7 days
Not Designated as Hedging Instrument [Member] \| Future [Member]
Notional Disclosures [Abstract]
Notional Amount	$ 29,100		$ 20,400
Fair Value
Asset			0
(Liability)	$ (188)		$ (188)
Weighted- Average Forward Price (in dollars per share)	$ 127.32	$ 121.09

Derivative, Weighted-Average Forward Price

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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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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- 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, before 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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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