Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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Disclosures about Fair Value of Assets and Liabilities - Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets and liabilities measured at fair value on a nonrecurring basis
Trading securities	$ 140,837	$ 137,675
Available for sale securities	408,371	325,874
Mortgage servicing rights	66,079	53,670	$ 55,553	$ 52,913
Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Trading securities	140,837	137,675
Mortgage servicing rights	66,079	53,670
Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Trading securities	140,837	137,675
Level 3 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Mortgage servicing rights	66,079	53,670
Treasury notes \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	992	999
Treasury notes \| Level 1 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	992	999
Federal agencies \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	374,731	288,993
Federal agencies \| Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	374,731	288,993
Mortgage-backed - Government-sponsored entity (GSE) - residential
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	25,960	26,382
Mortgage-backed - Government-sponsored entity (GSE) - residential \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	25,960	26,382
Mortgage-backed - Government-sponsored entity (GSE) - residential \| Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	25,960	26,382
Municipals \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	6,688	9,500
Municipals \| Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities		$ 9,500
Municipals \| Level 3 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	$ 6,688