Fair Value of Assets and Liabilities (Schedule of Valuation Techniques and Significant Unobservable Inputs Used to Measure Both Recurring and Nonrecurring) (Details) $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	$ 2,126,081	$ 1,803,666
Mortgage servicing rights	75,183	33,676	$ 19,103	$ 9,092
Impaired loans-collateral based	127,269	105,088
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans-collateral based	127,300
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment	93,857	33,717
Mortgage servicing rights	75,183	33,676
Derivatives	73,172	52,069
Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment	11,347	33,717
Mortgage servicing rights	75,183	33,676
Derivatives	2,457	2,157
Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans-collateral based	99,803
Other real estate owned, including covered other real-estate owned	24,820
Fair Value, Measurements, Nonrecurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans-collateral based	99,803
Other real estate owned, including covered other real-estate owned	24,820
Municipal
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	138,490	115,352
Municipal | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	138,490	115,352
Municipal | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	108,926	77,181
U.S. Government agencies
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	140,307	156,915
U.S. Government agencies | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	140,307	156,915
U.S. Government agencies | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	$ 3,150	$ 3,779
Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.06
Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.18
Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.0998
Discount rate | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.04
Discount rate | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.05
Discount rate | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0431
Discount rate | Discounted cash flows | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.04
Mortgage servicing rights, measurement input	0.06
Discount rate | Discounted cash flows | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.05
Mortgage servicing rights, measurement input	0.18
Discount rate | Discounted cash flows | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0431
Mortgage servicing rights, measurement input	0.0998
Credit spread | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.00
Credit spread | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.07
Credit spread | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0130
Credit spread | Discounted cash flows | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.00
Credit spread | Discounted cash flows | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.07
Credit spread | Discounted cash flows | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0130
Constant prepayment rate (CPR) | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.1206
Constant prepayment rate (CPR) | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.06
Constant prepayment rate (CPR) | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.91
Constant prepayment rate (CPR) | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.1176
Constant prepayment rate (CPR) | Discounted cash flows | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.1206
Constant prepayment rate (CPR) | Discounted cash flows | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.06
Constant prepayment rate (CPR) | Discounted cash flows | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.91
Constant prepayment rate (CPR) | Discounted cash flows | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.1206
Mortgage servicing rights, measurement input	0.1176
Cost of servicing | Discounted cash flows | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	15
Cost of servicing | Discounted cash flows | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	200
Cost of servicing | Discounted cash flows | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	77
Cost of servicing - delinquent | Discounted cash flows | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	200
Cost of servicing - delinquent | Discounted cash flows | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	1,000
Cost of servicing - delinquent | Discounted cash flows | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	273
Pull-through rate | Discounted cash flows | Minimum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives, measurement input	0.17
Pull-through rate | Discounted cash flows | Maximum | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives, measurement input	1.00
Pull-through rate | Discounted cash flows | Weighted Average | Fair Value, Measurements, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives, measurement input	0.8615
Appraisal adjustment - cost of sale | Appraisal value | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans - collateral based, measurement input	0.10
Other real estate owned, including covered other real-estate owned, measurement input	0.10
Appraisal adjustment - cost of sale | Appraisal value | Weighted Average | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans - collateral based, measurement input	0.1000
Other real estate owned, including covered other real-estate owned, measurement input	0.1000