Fair Value - Assets and liabilities measured at fair value on a recurring basis - (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Assets
Securities available for sale	$ 1,650,710	$ 999,405
Government-sponsored entities debt
Assets
Securities available for sale	85,509	84,642
State and municipal obligations
Assets
Securities available for sale	220,437	107,402
Common Stock
Assets
Securities available for sale	4,077	3,784
Parent company
Assets
Securities available for sale		631
Recurring basis
Assets
Derivative financial instruments	3,306	2,606
Loans held for sale	70,890	50,572
Securities available for sale	1,650,710	999,405
Mortgage servicing rights	31,119	29,037
Fair value of Assets, Total	1,756,025	1,081,620
Liabilities
Derivative financial instruments	3,248	730
Changes in fair value of assets
Transfers between the fair value hierarchy levels	0	0
Recurring basis \| Government-sponsored entities debt
Assets
Securities available for sale	85,509	84,642
Recurring basis \| State and municipal obligations
Assets
Securities available for sale	220,437	107,402
Recurring basis \| Mortgage-backed securities
Assets
Securities available for sale	1,340,687	803,577
Recurring basis \| Common Stock
Assets
Securities available for sale	4,077	3,784
Recurring basis \| Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Securities available for sale		2,559
Fair value of Assets, Total		2,559
Recurring basis \| Quoted Prices In Active Markets for Identical Assets (Level 1) \| Common Stock
Assets
Securities available for sale		2,559
Recurring basis \| Significant Other Observable Inputs (Level 2)
Assets
Derivative financial instruments	3,306	2,606
Loans held for sale	70,890	50,572
Securities available for sale	1,650,710	996,846
Fair value of Assets, Total	1,724,906	1,050,024
Liabilities
Derivative financial instruments	3,248	730
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Government-sponsored entities debt
Assets
Securities available for sale	85,509	84,642
Recurring basis \| Significant Other Observable Inputs (Level 2) \| State and municipal obligations
Assets
Securities available for sale	220,437	107,402
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities
Assets
Securities available for sale	1,340,687	803,577
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Common Stock
Assets
Securities available for sale	4,077	1,225
Recurring basis \| Significant Unobservable Inputs (Level 3)
Assets
Mortgage servicing rights	31,119	29,037
Fair value of Assets, Total	31,119	29,037
Changes in fair value of assets
Fair value of assets at the beginning of the period	29,037	26,202
Servicing assets that resulted from transfers of financial assets	6,439	6,428
Changes in fair value assets due to valuation inputs or assumptions	(595)	560
Changes in fair value assets due to increased principal paydowns	3,762	4,153
Fair value of assets at the end of the period	31,119	29,037
Unrealized losses included in accumulated other comprehensive income related to Level 3 financial assets and liabilities	$ 0	$ 0

Represents the amount of transfers between the fair value hierarchy.

No definition available.

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- Definition

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

+ References

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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- Definition

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
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-Paragraph 2
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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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-Paragraph 2
-Subparagraph (c)(2)
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- Definition

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
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-Subparagraph (c)
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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
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
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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)
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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.

+ References

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