Fair Value - Assets and liabilities measured at fair value on a recurring basis - (Details) - USD ($)	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Assets
Derivative financial instruments	$ 200,000
Securities available for sale	1,320,679,000	$ 925,374,000	$ 999,405,000
Liabilities
Derivative financial instruments	197,000
Government-sponsored entities debt
Assets
Securities available for sale	85,951,000	62,980,000	84,642,000
State and municipal obligations
Assets
Securities available for sale	204,294,000	117,324,000	107,402,000
Common Stock
Assets
Securities available for sale	2,957,000	3,793,000	3,784,000
Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	29,937,000	23,064,000	29,037,000
Changes in fair value of assets
Changes in hierarchy classifications of Level 3 liabilities	0
Recurring basis
Assets
Derivative financial instruments	1,492,000	3,091,000	2,606,000
Loans held for sale	46,321,000	57,052,000	50,572,000
Securities available for sale	1,320,679,000	925,374,000	999,405,000
Mortgage servicing rights	29,937,000	23,064,000	29,037,000
Fair value of Assets, Total	1,398,429,000	1,008,581,000	1,081,620,000
Liabilities
Derivative financial instruments	1,301,000	1,100,000	730,000
Recurring basis \| Government-sponsored entities debt
Assets
Securities available for sale	85,951,000	62,980,000	84,642,000
Recurring basis \| State and municipal obligations
Assets
Securities available for sale	204,294,000	117,324,000	107,402,000
Recurring basis \| Mortgage-backed securities
Assets
Securities available for sale	1,027,477,000	741,277,000	803,577,000
Recurring basis \| Common Stock
Assets
Securities available for sale	2,957,000	3,793,000	3,784,000
Recurring basis \| Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Securities available for sale	1,732,000	2,568,000	2,559,000
Fair value of Assets, Total	1,732,000	2,568,000	2,559,000
Recurring basis \| Quoted Prices In Active Markets for Identical Assets (Level 1) \| Common Stock
Assets
Securities available for sale	1,732,000	2,568,000	2,559,000
Recurring basis \| Significant Other Observable Inputs (Level 2)
Assets
Derivative financial instruments	1,492,000	3,091,000	2,606,000
Loans held for sale	46,321,000	57,052,000	50,572,000
Securities available for sale	1,318,947,000	922,806,000	996,846,000
Fair value of Assets, Total	1,366,760,000	982,949,000	1,050,024,000
Liabilities
Derivative financial instruments	1,301,000	1,100,000	730,000
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Government-sponsored entities debt
Assets
Securities available for sale	85,951,000	62,980,000	84,642,000
Recurring basis \| Significant Other Observable Inputs (Level 2) \| State and municipal obligations
Assets
Securities available for sale	204,294,000	117,324,000	107,402,000
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities
Assets
Securities available for sale	1,027,477,000	741,277,000	803,577,000
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Common Stock
Assets
Securities available for sale	1,225,000	1,225,000	1,225,000
Recurring basis \| Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	29,937,000	23,064,000	29,037,000
Fair value of Assets, Total	29,937,000	23,064,000	$ 29,037,000
Changes in fair value of assets
Fair value of assets at the beginning of the period	29,037,000	26,202,000
Servicing assets that resulted from transfers of financial assets	4,764,000	4,182,000
Changes in fair value assets due to valuation inputs or assumptions	(1,055,000)	(4,305,000)
Changes in fair value assets due to increased principal paydowns	2,809,000	3,015,000
Fair value of assets at the end of the period	29,937,000	23,064,000
Unrealized losses included in accumulated other comprehensive income related to Level 3 financial assets and liabilities	$ 0	$ 0

Represents the amount of servicing assets that resulted from transfers of financial assets.

No definition available.

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- Definition

The element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, the element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. The item represents residential mortgage servicing rights as presented on the statement of financial position which are due to the entity as of the balance sheet date.

+ References

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

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

+ References

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)
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
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- Definition

Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets, liabilities and financial instruments classified in shareholders' equity measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy.

+ References

No definition available.

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- Definition

Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

+ 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)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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- Definition

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

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