Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Fixed income			$ 167,882	$ 216,625	$ 268,561
Deposit transactions and cash management			133,281	110,592	108,553
Brokerage, management fees and commissions			54,803	48,514	42,911
Trust services and investment management			29,806	28,420	27,727
Bankcard income			26,718	25,467	24,430
Bank-owned life insurance (BOLI)			18,955	15,124	14,687
Debt securities gains/(losses), net			52	483	1,485
Equity securities gains/(losses), net			212,896	109	(144)
Other income/(loss)			78,395	44,885	64,231
Total noninterest income			722,788	490,219	552,441
Gain on sale of TRUPs loans			3,777	0	0
All other income and commissions			1,320	(6,657)	(3,447)
Visa Class B Shares
Disaggregation of Revenue [Line Items]
Gain on sale of investments	$ 212,900		212,900
Underwriting, Portfolio Advisory, and Other Noninterest Income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer			28,900
Regional Banking
Disaggregation of Revenue [Line Items]
Fixed income			417	430	79
Deposit transactions and cash management			126,909	105,163	103,122
Brokerage, management fees and commissions			54,800	48,513	42,911
Trust services and investment management			29,852	28,491	27,764
Bankcard income			26,848	25,014	23,945
Bank-owned life insurance (BOLI)			0	0	0
Debt securities gains/(losses), net			0	386	0
Equity securities gains/(losses), net			0	0	0
Other income/(loss)			70,482	50,630	51,175
Total noninterest income			309,308	258,627	248,996
Fixed Income
Disaggregation of Revenue [Line Items]
Fixed income			163,382	216,195	268,482
Deposit transactions and cash management			12	3	3
Brokerage, management fees and commissions			0	0	0
Trust services and investment management			0	0	0
Bankcard income			0	0	0
Bank-owned life insurance (BOLI)			0	0	0
Debt securities gains/(losses), net			0	0	0
Equity securities gains/(losses), net			0	0	0
Other income/(loss)			1,373	884	859
Total noninterest income			164,767	217,082	269,344
Corporate
Disaggregation of Revenue [Line Items]
Fixed income			0	0	0
Deposit transactions and cash management			6,144	5,236	5,250
Brokerage, management fees and commissions			0	1	0
Trust services and investment management			(46)	(71)	(37)
Bankcard income			226	225	215
Bank-owned life insurance (BOLI)			18,955	15,124	14,687
Debt securities gains/(losses), net			52	97	1,485
Equity securities gains/(losses), net			212,896	109	(144)
Other income/(loss)			1,025	(11,843)	(1,003)
Total noninterest income			239,252	8,878	20,453
(Gain)/loss on securities		$ 14,300		14,300
Non-Strategic
Disaggregation of Revenue [Line Items]
Fixed income			4,083	0	0
Deposit transactions and cash management			216	190	178
Brokerage, management fees and commissions			3	0	0
Trust services and investment management			0	0	0
Bankcard income			(356)	228	270
Bank-owned life insurance (BOLI)			0	0	0
Debt securities gains/(losses), net			0	0	0
Equity securities gains/(losses), net			0	0	0
Other income/(loss)			5,515	5,214	13,200
Total noninterest income			9,461	$ 5,632	$ 13,648
Gain on sale of TRUPs loans			$ 4,100

Bankcard Other Income

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Acting as an agent, a broker-dealer may buy and sell securities on behalf of its customers. In return for such services, the broker-dealer charges a commission. Each time a customer enters into a buy or sell transaction, a commission is earned by the broker-dealer for its selling and administrative efforts. For securities purchased, the commission is recorded as a receivable from customers; for securities sold, it is recorded as reductions in the payable to customers. Commissions earned are usually related to the broker-dealer's customers' trading volume and the dollar amounts of the trades. In general, commissions are for smaller trades of exchange-listed stocks and bonds made by retail customers. Revenue recognized in the period for (1) performance (incentive) fees based on the investment results achieved for management of certain institutional accounts and hedge funds, (2) schedule-based fees earned for management of mutual funds and closed-end funds, based either on average daily net assets or on a combination of the average daily net assets and gross income, and (3) other investment management and advisory fees.

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Deposit transactions and cash management.

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The major component of revenue in this line item is generated from the purchase and sale of securities as both principal and agent, and from other fee sources including loan sales, portfolio advisory, and derivative sales.

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No definition available.

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Gain On Sale Of Held-To-Maturity Loans

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Trust Services And Investment Management

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- Definition

Earnings on or other increases in the value of the cash surrender value of bank owned life insurance policies.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13)
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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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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.

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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
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The difference between the carrying value and the sale price of equity securities, not separately or otherwise categorized as trading or available-for-sale. This element includes investments in which the entity holds a small ownership stake (generally, less than 20% of the shares outstanding) and cannot exert significant influence.

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No definition available.

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Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

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The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale.

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- Definition

The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

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Amount of revenue earned, classified as other, excluding interest income.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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