Fair Value Measurement - FV of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Investment securities held to maturity	$ 76,782	$ 58,128
Fair value of loans held for investment	4,187	5,477
Loans held for sale, fair value option	527,088	577,313
Mortgage servicing rights	245,744	258,560
Carrying value [Member]
Assets:
Cash and cash equivalents	176,218	72,718
Investment securities held to maturity	78,035	58,036
Fair value of loans held for investment	4,879,123	4,500,989
Loans held for sale - transferred from held for investment	1,517
Federal Home Loan Bank Stock	48,157	46,639
Liabilities:
Time deposits	1,396,082	1,190,689
Federal Home Loan Bank advances	1,008,613	979,201
Other borrowings	30,007
Long-term debt	125,368	125,274
Fair value [Member]
Assets:
Cash and cash equivalents	176,218	72,718
Investment securities held to maturity	76,783	58,128
Fair value of loans held for investment	4,855,496	4,497,884
Loans held for sale - transferred from held for investment	1,517
Federal Home Loan Bank Stock	48,157	46,639
Liabilities:
Time deposits	1,388,422	1,186,126
Federal Home Loan Bank advances	1,010,460	981,441
Other borrowings	30,007
Long-term debt	107,418	108,530
Level 1 [Member] \| Fair value [Member]
Assets:
Cash and cash equivalents	176,218	72,718
Investment securities held to maturity	0	0
Fair value of loans held for investment	0	0
Loans held for sale - transferred from held for investment	0
Federal Home Loan Bank Stock	0	0
Liabilities:
Time deposits	0	0
Federal Home Loan Bank advances	0	0
Other borrowings	30,007
Long-term debt	0	0
Level 2 [Member] \| Fair value [Member]
Assets:
Cash and cash equivalents	0	0
Investment securities held to maturity	76,783	58,128
Fair value of loans held for investment	0	0
Loans held for sale - transferred from held for investment	0
Federal Home Loan Bank Stock	48,157	46,639
Liabilities:
Time deposits	1,388,422	1,186,126
Federal Home Loan Bank advances	1,010,460	981,441
Other borrowings	0
Long-term debt	107,418	108,530
Level 3 [Member] \| Fair value [Member]
Assets:
Cash and cash equivalents	0	0
Investment securities held to maturity	0	0
Fair value of loans held for investment	4,855,496	4,497,884
Loans held for sale - transferred from held for investment	1,517
Federal Home Loan Bank Stock	0	0
Liabilities:
Time deposits	0	0
Federal Home Loan Bank advances	0	0
Other borrowings	0
Long-term debt	0	0
Multifamily [Member] \| Carrying value [Member]
Assets:
Loans held for sale, fair value option	39,909	33,589
Mortgage servicing rights	26,461	26,093
Multifamily [Member] \| Fair value [Member]
Assets:
Loans held for sale, fair value option	39,909	33,589
Mortgage servicing rights	29,006	28,362
Multifamily [Member] \| Level 1 [Member] \| Fair value [Member]
Assets:
Loans held for sale, fair value option	0	0
Mortgage servicing rights	0	0
Multifamily [Member] \| Level 2 [Member] \| Fair value [Member]
Assets:
Loans held for sale, fair value option	39,909	33,589
Mortgage servicing rights	0	0
Multifamily [Member] \| Level 3 [Member] \| Fair value [Member]
Assets:
Loans held for sale, fair value option	0	0
Mortgage servicing rights	$ 29,006	$ 28,362

Other Borrowings, Fair Value Disclosure

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- Definition

Portfolio loans transferred to held for sale, fair value disclosure

+ References

No definition available.

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

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- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75030709&loc=d3e39828-111592

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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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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