Fair Value of Assets and Liabilities (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) $ / Loan	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 2,126,081,000	$ 1,803,666,000
Mortgage servicing rights	75,183,000	33,676,000	$ 19,103,000	$ 9,092,000
Mortgage loans held-for-sale	264,070,000	313,592,000
Impaired loans	$ 127,269,000	105,088,000
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pull through rate, derivatives (as a percent)	17.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pull through rate, derivatives (as a percent)	100.00%
Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pull through rate, derivatives (as a percent)	86.15%
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 2,126,081,000	1,803,666,000
Mortgage servicing rights	75,183,000	33,676,000
Principal amount outstanding on loans held-for-sale or securitization or asset-backed financing arrangement	253,700,000	299,500,000
Mortgage loans held-for-sale	264,070,000	313,592,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	127,300,000
Level 3 | Valued Using Discounted Cash Flow Model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	27,500,000
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	138,490,000	115,352,000
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	140,307,000	156,915,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment	93,857,000	33,717,000
Mortgage servicing rights	75,183,000	33,676,000
Derivative Assets	73,172,000	52,069,000
Mortgage loans held-for-sale	264,070,000	313,592,000
Fair Value, Measurements, Recurring | Non-performing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held-for-sale	1,900,000.0	0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment	11,347,000	33,717,000
Mortgage servicing rights	75,183,000	33,676,000
Derivative Assets	2,457,000	2,157,000
Mortgage loans held-for-sale	$ 0	0
Fair Value, Measurements, Recurring | Level 3 | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights, measurement input	0.06
Fair Value, Measurements, Recurring | Level 3 | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights, measurement input	0.18
Fair Value, Measurements, Recurring | Level 3 | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights, measurement input	0.0998
Fair Value, Measurements, Recurring | Level 3 | Mortgage Servicing Rights | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost of servicing loan (in dollars per loan) | $ / Loan	77.00
Cost of servicing delinquent loan (in dollars per loan) | $ / Loan	273
Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 138,490,000	115,352,000
Fair Value, Measurements, Recurring | Municipal | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	108,926,000	77,181,000
Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	140,307,000	156,915,000
Fair Value, Measurements, Recurring | U.S. Government agencies | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,150,000	$ 3,779,000
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	99,803,000
Other real estate owned	24,820,000
Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	99,803,000
Other real estate owned	$ 24,820,000
Discount rate | Fair Value, Measurements, Recurring | Level 3 | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.04
Discount rate | Fair Value, Measurements, Recurring | Level 3 | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.05
Discount rate | Fair Value, Measurements, Recurring | Level 3 | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.0431
Constant prepayment rate (CPR) | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.1206
Constant prepayment rate (CPR) | Fair Value, Measurements, Recurring | Level 3 | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights, measurement input	0.06
Constant prepayment rate (CPR) | Fair Value, Measurements, Recurring | Level 3 | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights, measurement input	0.91
Constant prepayment rate (CPR) | Fair Value, Measurements, Recurring | Level 3 | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights, measurement input	0.1176
Credit spread | Fair Value, Measurements, Recurring | Level 3 | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.00
Credit spread | Fair Value, Measurements, Recurring | Level 3 | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.07
Credit spread | Fair Value, Measurements, Recurring | Level 3 | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment, measurement input	0.0130
Appraisal value | Appraisal adjustment - cost of sale | Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate owned, including covered other real-estate owned, measurement input	0.10
Appraisal value | Appraisal adjustment - cost of sale | Fair Value, Measurements, Nonrecurring | Level 3 | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate owned, including covered other real-estate owned, measurement input	0.1000