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Significant Accounting Policies - Impact of new financial accounting standards (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Recently Issued Accounting Standards
Lease, Practical Expedients, Package [true/false]	true
Lease, Practical Expedient, Use of Hindsight [true/false]	false
Right of use asset	$ 10,898
Lease liability	10,982
Accounting Standards Update 2017-12
Recently Issued Accounting Standards
Transferred securities from held to maturity to available-for-sale	$ 573,600
Accounting Standards Update 2016-02 | Restatement
Recently Issued Accounting Standards
Right of use asset		$ 11,600
Lease liability		$ 9,700

X

- Definition

Amount of investment in debt security, measured at amortized cost, transferred to investment in debt security, measured at fair value, with change in fair value recognized in other comprehensive income (available-for-sale) and net income (trading).

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

X

- Definition

Indicates (true/false) whether practical expedient is elected to use hindsight in determining lease term and in assessing impairment of right-of-use asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=84153547&loc=SL77916155-209984

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84153547&loc=SL77916155-209984

+ Details

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X

- Definition

Indicates (true/false) whether practical expedients are elected for not reassessing whether any expired or existing contract is or contains lease, lease classification for expired or existing lease, and initial direct costs for any existing lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=84153547&loc=SL77916155-209984

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=84153547&loc=SL77916155-209984

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X

- 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.

+ Details

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X

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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