Fair Value Measurements - Gains and Losses Included in Earnings Related to Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Non-interest Income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Total gains (losses) included in earnings	$ (1,166)
Change in unrealized gains (losses) relating to assets still held at December 31, 2017	0
Other Comprehensive Income (loss) net of tax
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Total gains (losses) included in earnings	0
Change in unrealized gains (losses) relating to assets still held at December 31, 2017	$ (11,721)

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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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

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
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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