This is the sum of principal amount outstanding for both securitized and unsecuritized loans of all types.

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Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Reflects the estimated amount of impairment as of the balance sheet date of recognized servicing assets that are being amortized in proportion to and over the period of estimated net servicing income or loss.

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Summary of Significant Accounting Policies (Mortgage Servicing and Transfers of Financial Assets and Servicing Rights, Net) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	May 18, 2018	Dec. 31, 2017	Dec. 31, 2016
Servicing Asset at Amortized Cost [Line Items]
Aggregate unpaid principal balance	$ 4,100,000		$ 3,560,000
Mortgage Servicing Rights
Servicing Asset at Amortized Cost [Line Items]
Servicing asset	29,363		23,248	$ 32,088
Fair value of mortgage servicing rights	48,680		37,081
Mortgage Servicing Rights 15 Year
Servicing Asset at Amortized Cost [Line Items]
Servicing rights, valuation allowance			20
Mortgage Servicing Rights 30 Year
Servicing Asset at Amortized Cost [Line Items]
Servicing rights, valuation allowance			38
Commercial Servicing Rights more than 20 Years
Servicing Asset at Amortized Cost [Line Items]
Servicing asset	1,414		2,084
Fair value of mortgage servicing rights	1,643		2,481
Servicing rights, valuation allowance	$ 0		$ 12
First Bank Lubbock Bancshares, Inc. \| Mortgage Servicing Rights
Servicing Asset at Amortized Cost [Line Items]
Servicing asset		$ 640,700
Fair value of mortgage servicing rights		$ 7,000