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Fair Value of Financial Instruments - Changes in the Level 3 Fair Value Category of Unobservable Inputs (Detail) - USD ($) $ in Thousands | 6 Months Ended
--- | ---
Jun. 30, 2018 | Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | $ 196,398 |
Ending Balance | 187,036 |
Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 1,428 |
Ending Balance | 1,410 |
Level 3 [Member] | State and Local Governments [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 1,428 | $ 1,418
Change in Market Value | (18) | 30
Payments & Maturities | 0 | 0
Ending Balance | 1,410 | 1,448
Level 3 [Member] | State and Local Governments [Member] | Tax - Exempt [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Payments & Maturities | 0 | 0
Level 3 [Member] | State and Local Governments [Member] | Taxable [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Beginning Balance | 1,428 | 1,418
Change in Market Value | (18) | 30
Payments & Maturities | 0 | 0
Ending Balance | $ 1,410 | $ 1,448

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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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. + Details
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