Subsequent events Subsequent events (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Jul. 01, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Business Combination, Consideration Transferred	$ 86,203,000
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	48,519,000
Payments to Acquire Businesses, Gross	30,684,000
Deposits	$ 6,279,326,000		$ 5,817,326,000
Common Stock, Par or Stated Value Per Share	$ 1.00
Business Acquisition, Share Price	3.80	$ 1.08
Investment Options, Exercise Price	$ 19.00
Liabilities Subject to Compromise, Early Contract Termination Fees	$ 5,317,500
Common Stock [Member]
Subsequent Event [Line Items]
Business Acquisition, Share Price	$ 0.1378	$ 0.01

Exercise price of the option.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Footnote 5

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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

+ References

No definition available.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
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-Paragraph 8
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Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

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Face amount or stated value per share of common stock.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
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Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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