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Significant Accounting Policies - Impact of new financial accounting standards (Details) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2019 USD ($) | Dec. 31, 2019 USD ($) | Jan. 01, 2019 USD ($)
Recently Issued Accounting Standards |  |  |
Lease, Practical Expedients, Package [true false] |  | true |
Lease, Practical Expedient, Use of Hindsight [true false] |  | false |
Right of use asset |  | $ 9,490 |
Lease liability |  | $ 9,552 |
Allowance for credit losses | Credit concentration risk | Minimum |  |  |
Recently Issued Accounting Standards |  |  |
Percentage increase in reserve for unfunded commitments above the existing allowance for loan loss levels |  | 25 |
Allowance for credit losses | Credit concentration risk | Maximum |  |  |
Recently Issued Accounting Standards |  |  |
Percentage increase in reserve for unfunded commitments above the existing allowance for loan loss levels |  | 45 |
Accounting Standards Update 2016-02 | Restatement |  |  |
Recently Issued Accounting Standards |  |  |
Right of use asset |  |  | $ 8,100
Lease liability |  |  | $ 8,100
Accounting Standards Update 2017-12 |  |  |
Recently Issued Accounting Standards |  |  |
Transferred securities from held to maturity to available-for-sale | $ 573,600 | $ 0 |

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- 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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 10 -Section 65 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 10 -Section 65 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984 + Details
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