Fair Value Measurements - Carrying Amounts and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investment securities:
Held-to-maturity	$ 598,197	$ 662,906
Level 3 \| Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	74,980	73,518
Level 3 \| Nonrecurring \| Impaired loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	73,137	70,619
Carrying Amount \| Level 2
Investment securities:
Held-to-maturity	607,867	676,593
Financial liabilities:
Time deposits	3,865,489	3,217,207
Collateralized customer deposits	377,471	415,236
Short-term borrowings	1,670,000	2,000,000
Long-term borrowings	430,971	372,882
Carrying Amount \| Level 3
Investment securities:
Held-to-maturity	500	500
Net loans	14,692,211	14,063,380
Fair Value \| Level 2
Investment securities:
Held-to-maturity	597,747	662,516
Financial liabilities:
Time deposits	3,827,695	3,225,847
Collateralized customer deposits	376,969	415,236
Short-term borrowings	1,669,662	1,999,137
Long-term borrowings	426,105	367,984
Fair Value \| Level 3
Investment securities:
Held-to-maturity	450	390
Net loans	$ 14,301,208	$ 14,114,545

Collateralized Customer Deposits, Fair Value Disclosure

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- Definition

Investment securities.

+ References

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- Definition

Fair value portion of time deposits.

+ References

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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