Fair Value of Assets & Liabilities - Schedule Of Unobservable Inputs Utilized In Determining The Fair Value Of Level 3 Recurring And Non-Recurring Measurements (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale	$ 4,608,383	$ 5,170,255
Loans held-for-sale (elected fair value)	16,418	20,881
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	34,212	5,645
Loans, net of unearned income, fair value disclosure	26,995	26,666
OREO, fair value disclosure	25,726	39,566
Level 3 | Loans held- for-sale | Residential Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale (elected fair value)	16,778	19,544
Level 3 | Loans held-for-sale- unguaranteed interest in SBA loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale (elected fair value)	1,018	1,473
Level 3 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	23,329	26,521
Level 3 | Interest- only strips- AFS | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale	$ 10,361	$ 1,270
Constant prepayment rate | Level 3 | Discounted cash flow | Minimum | Loans held-for-sale- unguaranteed interest in SBA loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.08	0.08
Constant prepayment rate | Level 3 | Discounted cash flow | Maximum | Loans held-for-sale- unguaranteed interest in SBA loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.12	0.12
Constant prepayment rate | Level 3 | Interest- only strips- AFS | Discounted cash flow | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities, measurement input	0.11
Constant prepayment rate | Level 3 | Interest- only strips- AFS | Discounted cash flow | Minimum | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities, measurement input		0.10
Constant prepayment rate | Level 3 | Interest- only strips- AFS | Discounted cash flow | Maximum | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities, measurement input		0.11
Bond equivalent yield | Level 3 | Discounted cash flow | Loans held-for-sale- unguaranteed interest in SBA loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.09
Bond equivalent yield | Level 3 | Discounted cash flow | Minimum | Loans held-for-sale- unguaranteed interest in SBA loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input		0.09
Bond equivalent yield | Level 3 | Discounted cash flow | Maximum | Loans held-for-sale- unguaranteed interest in SBA loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input		0.10
Bond equivalent yield | Level 3 | Interest- only strips- AFS | Discounted cash flow | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities, measurement input		0.17
Bond equivalent yield | Level 3 | Interest- only strips- AFS | Discounted cash flow | Minimum | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities, measurement input	0.13
Bond equivalent yield | Level 3 | Interest- only strips- AFS | Discounted cash flow | Maximum | Available-for-sale- securities SBA-interest only strips
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities, measurement input	0.18
Prepayment speeds - First mortgage | Level 3 | Discounted cash flow | Minimum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.02	0.02
Prepayment speeds - First mortgage | Level 3 | Discounted cash flow | Maximum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.11	0.12
Prepayment speeds - HELOC | Level 3 | Discounted cash flow | Minimum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.05	0.05
Prepayment speeds - HELOC | Level 3 | Discounted cash flow | Maximum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.12	0.12
Foreclosure losses | Level 3 | Discounted cash flow | Minimum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.50	0.50
Foreclosure losses | Level 3 | Discounted cash flow | Maximum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.70	0.70
Loss severity trends - First mortgage | Level 3 | Discounted cash flow | Minimum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.02	0.05
Loss severity trends - First mortgage | Level 3 | Discounted cash flow | Maximum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.25	0.30
Loss severity trends - HELOC | Level 3 | Discounted cash flow | Minimum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	0.50	0.15
Loss severity trends - HELOC | Level 3 | Discounted cash flow | Maximum | Loans held- for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale, measurement input	1.00	1.00
Visa covered litigation resolution amount | Level 3 | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ 5,200,000	$ 4,400,000
Visa covered litigation resolution amount | Level 3 | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ 5,800,000	$ 5,200,000
Probability of resolution scenarios | Level 3 | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	0.20	0.10
Probability of resolution scenarios | Level 3 | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	0.30	0.30
Time until resolution | Level 3 | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, term	24 months	18 months
Time until resolution | Level 3 | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, term	48 months	48 months
Marketability adjustments for specific properties | Level 3 | Appraisals from comparable properties | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans net of unearned income, measurement input	0.00	0.00
Marketability adjustments for specific properties | Level 3 | Appraisals from comparable properties | Minimum | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value disclosure	0.00	0.00
Marketability adjustments for specific properties | Level 3 | Appraisals from comparable properties | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans net of unearned income, measurement input	0.10	0.10
Marketability adjustments for specific properties | Level 3 | Appraisals from comparable properties | Maximum | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value disclosure	0.25	0.25
Borrowing base certificates adjustment | Level 3 | Other collateral valuations | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans net of unearned income, measurement input	0.20	0.20
Borrowing base certificates adjustment | Level 3 | Other collateral valuations | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans net of unearned income, measurement input	0.50	0.50
Financial Statements/Auction values adjustment | Level 3 | Other collateral valuations | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans net of unearned income, measurement input	0.00	0.00
Financial Statements/Auction values adjustment | Level 3 | Other collateral valuations | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans net of unearned income, measurement input	0.25	0.25
Adjustment for value changes since appraisal | Level 3 | Appraisals from comparable properties | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
OREO, measurement input	0.00	0.00
Adjustment for value changes since appraisal | Level 3 | Appraisals from comparable properties | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
OREO, measurement input	0.10	0.10
Adjustments to current sales yields for specific properties | Level 3 | Discounted cash flow | Minimum | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value disclosure	0.00	0.00
Adjustments to current sales yields for specific properties | Level 3 | Discounted cash flow | Maximum | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets, fair value disclosure	0.15	0.15