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Investments - Schedule of Available for Sale Securities Continuous Unrealized Loss Position Fair Value (Details) $ in Thousands | Jun. 30, 2018 USD ($) Number | Dec. 31, 2017 USD ($) Number
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Debt Securities, Available-for-sale [Line Items] |  |
No. of securities | Number | 526 | 345
Fair value, Less than 12 months | $ 234,778 | $ 134,700
Unrealized losses, Less than 12 months | (4,272) | (1,022)
Fair value, 12 months or longer | 91,448 | 89,790
Unrealized losses, 12 months or longer | (3,565) | (2,001)
Total, Fair value | 326,226 | 224,490
Total, Unrealized losses | $ (7,837) | $ (3,023)
US Treasury Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
No. of securities | Number | 1 | 1
Fair value, Less than 12 months | $ 1,952 | $ 1,990
Unrealized losses, Less than 12 months | (47) | (9)
Fair value, 12 months or longer |  |
Unrealized losses, 12 months or longer |  |
Total, Fair value | 1,952 | 1,990
Total, Unrealized losses | $ (47) | $ (9)
US Federal Agency Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
No. of securities | Number | 11 | 14
Fair value, Less than 12 months | $ 3,723 | $ 7,989
Unrealized losses, Less than 12 months | (31) | (24)
Fair value, 12 months or longer | 9,729 | 8,272
Unrealized losses, 12 months or longer | (69) | (61)
Total, Fair value | 13,452 | 16,261
Total, Unrealized losses | $ (100) | $ (85)
Municipal Obligations, Tax Exempt [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
No. of securities | Number | 301 | 178
Fair value, Less than 12 months | $ 89,803 | $ 37,299
Unrealized losses, Less than 12 months | (1,508) | (273)
Fair value, 12 months or longer | 33,670 | 31,930
Unrealized losses, 12 months or longer | (1,598) | (807)
Total, Fair value | 123,473 | 69,229
Total, Unrealized losses | $ (3,106) | $ (1,080)
Municipal Obligations, Taxable [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
No. of securities | Number | 110 | 73
Fair value, Less than 12 months | $ 36,430 | $ 18,792
Unrealized losses, Less than 12 months | (531) | (96)
Fair value, 12 months or longer | 10,984 | 9,744
Unrealized losses, 12 months or longer | (177) | (120)
Total, Fair value | 47,414 | 28,536
Total, Unrealized losses | $ (708) | $ (216)
Agency Mortgage-backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
No. of securities | Number | 103 | 79
Fair value, Less than 12 months | $ 102,870 | $ 68,630
Unrealized losses, Less than 12 months | (2,155) | (620)
Fair value, 12 months or longer | 37,065 | 39,844
Unrealized losses, 12 months or longer | (1,721) | (1,013)
Total, Fair value | 139,935 | 108,474
Total, Unrealized losses | $ (3,876) | $ (1,633)

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References No definition available. + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References No definition available. + Details
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