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Commitments and Contingencies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Commitments [Line Items]
Data processing and communication expense	$ 10,400,000	$ 10,400,000	$ 11,700,000
Merger-related expenses included in data processing and communication charges	0	0	$ 1,300,000
Unfunded Loan Commitment
Other Commitments [Line Items]
Allowance for unfunded commitments	$ 2,200,000	$ 2,600,000

X

- Definition

Data processing contract termination and conversion cost expenses.

+ References

No definition available.

+ Details

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X

- Definition

The amount of expense in the period for communications and data processing expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

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