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Investments - Schedule of Available-for-sale Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | $ 385,833 | $ 388,520
Gross unrealized gains | 235 | 2,486
Gross unrealized losses | (10,029) | (3,023)
Estimated fair value | 376,039 | 387,983
US Treasury Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 1,999 | 1,999
Gross unrealized gains |  |
Gross unrealized losses | (56) | (9)
Estimated fair value | 1,943 | 1,990
US Federal Agency Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 15,177 | 16,572
Gross unrealized gains | 2 | 5
Gross unrealized losses | (90) | (85)
Estimated fair value | 15,089 | 16,492
Municipal Obligations, Tax Exempt [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 161,474 | 183,846
Gross unrealized gains | 148 | 1,972
Gross unrealized losses | (4,365) | (1,080)
Estimated fair value | 157,257 | 184,738
Municipal Obligations, Taxable [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 53,834 | 57,783
Gross unrealized gains | 81 | 409
Gross unrealized losses | (924) | (216)
Estimated fair value | 52,991 | 57,976
Agency Mortgage-backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 145,569 | 119,096
Gross unrealized gains | 4 | 92
Gross unrealized losses | (4,594) | (1,633)
Estimated fair value | 140,979 | 117,555
Certificates of Deposit [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 7,780 | 9,224
Gross unrealized gains |  |
Gross unrealized losses |  |
Estimated fair value | $ 7,780 | 9,224
Common Stocks [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost |  |
Gross unrealized gains |  | 8
Gross unrealized losses |  |
Estimated fair value |  | $ 8

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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