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Disclosures about Fair Value of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosures about Fair Value of Assets and Liabilities
Trading securities	$ 269,891	$ 163,419
Available for sale securities	290,243	331,071
Loans held for sale	19,592	11,886
Mortgage servicing rights	74,387	77,844	$ 66,079	$ 53,670
Recurring
Disclosures about Fair Value of Assets and Liabilities
Trading securities	269,891	163,419
Loans held for sale	19,592	11,886
Mortgage servicing rights	74,387	77,844
Recurring \| Interest Rate Lock Commitments
Disclosures about Fair Value of Assets and Liabilities
Derivative assets	186	70
Recurring \| Forward Contracts
Disclosures about Fair Value of Assets and Liabilities
Derivative liabilities	27	9
Recurring \| Interest rate swaps
Disclosures about Fair Value of Assets and Liabilities
Derivative assets	511
Derivative liabilities	511
Level 2 \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Trading securities	269,891	163,419
Loans held for sale	19,592	11,886
Level 2 \| Recurring \| Forward Contracts
Disclosures about Fair Value of Assets and Liabilities
Derivative liabilities	27	9
Level 2 \| Recurring \| Interest rate swaps
Disclosures about Fair Value of Assets and Liabilities
Derivative assets	511
Derivative liabilities	511
Level 3 \| Interest Rate Lock Commitments
Disclosures about Fair Value of Assets and Liabilities
Derivative assets	186	70
Level 3 \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Mortgage servicing rights	74,387	77,844
Level 3 \| Recurring \| Interest Rate Lock Commitments
Disclosures about Fair Value of Assets and Liabilities
Derivative assets	186	70
Treasury notes \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	4,765	11,941
Treasury notes \| Level 1 \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	4,765	11,941
Federal agencies
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	244,973	236,930
Federal agencies \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	244,973	236,930
Federal agencies \| Level 2 \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	244,973	236,930
Municipals \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	5,937	21,332
Municipals \| Level 2 \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	5,937	21,332
Mortgage-backed - Government-sponsored entity (GSE) - residential
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	34,568	60,868
Mortgage-backed - Government-sponsored entity (GSE) - residential \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	34,568	60,868
Mortgage-backed - Government-sponsored entity (GSE) - residential \| Level 2 \| Recurring
Disclosures about Fair Value of Assets and Liabilities
Available for sale securities	$ 34,568	$ 60,868