Disclosures about Fair Value of Assets and Liabilities - Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets and liabilities measured at fair value on a nonrecurring basis
Trading securities	$ 121,360	$ 137,675
Available for sale securities	430,581	325,874
Mortgage servicing rights	62,022	53,670
Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Trading securities	121,360	137,675
Mortgage servicing rights	62,022	53,670
Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Trading securities	121,360	137,675
Level 3 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Mortgage servicing rights	62,022	53,670
Treasury notes \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	997	999
Treasury notes \| Level 1 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	997	999
Federal agencies \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	403,517	288,993
Federal agencies \| Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	403,517	288,993
Mortgage-backed - Government-sponsored entity (GSE) - residential
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities	26,067	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	26,067	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	$ 26,067	26,382
Municipals \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities		9,500
Municipals \| Level 2 \| Recurring
Assets and liabilities measured at fair value on a nonrecurring basis
Available for sale securities		$ 9,500

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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