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Organization (Details)	12 Months Ended
Organization (Details)	Dec. 31, 2017 USD ($) reportable_segment acquisition bank_branch	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Number of Businesses Acquired \| acquisition	29
Loans Receivable Held-for-sale, Amount	$ 1,500,000,000
Transfer of Portfolio Loans and Leases to Held-for-sale	481,100,000	$ 0	$ 0
Loans held for sale, at lower of cost or fair value	481,100,000	0
Proceeds from Sale and Collection of Lease Receivables	0	$ 138,955,000	$ 0
New Accounting Pronouncement Or Change In Accounting Principle Effect Of Change of Income Taxes	$ 1,500,000
Allowance For Credit Losses, Look-back Period for Estimation	31	27
Fair Value Hedges, Net	$ 0
Derivative, Notional Amount	$ 91,100,000
Number of Reportable Segments \| reportable_segment	1
FDIC Insurance Limits	$ 250,000
Core Deposits [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 years
Core Deposits [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Customer Relationships [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	4 years
Customer Relationships [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 years
Furniture and Fixtures [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Building [Member]
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	35 years
Equity Securities [Member] \| Equity Method Investments [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Equity Securities [Member] \| Equity Method Investments [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Limited Partner [Member] \| Equity Method Investments [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	5.00%
Loans Under $250,000
Business Acquisition [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	$ 250,000
CALIFORNIA
Business Acquisition [Line Items]
Retail Branch Locations \| bank_branch	76
NORTH CAROLINA
Business Acquisition [Line Items]
Retail Branch Locations \| bank_branch	1
Expired Policies [Member]
Business Acquisition [Line Items]
Time Deposits, Less than $100,000	$ 100,000
Time Deposits, $100,000 or More	100,000
New Policies [Member]
Business Acquisition [Line Items]
Time Deposits, Less Than $250,000	250,000
Time Deposits, $250,000 or More	250,000
Retained Earnings [Member]
Business Acquisition [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	(420,000)
Cash Flow [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Loans Held-for-sale	$ 1,000,000,000
Performance Shares [Member]
Business Acquisition [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Performance Period	3 years
Share-based Compensation Award, Tranche One [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	150.00%
Share-based Compensation Award, Tranche Two [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	200.00%