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Investments - Maturity Table (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 182,325	$ 247,607
Estimated Fair Value	176,245	$ 244,088
Maturity 2038
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	265
Estimated Fair Value	279
Maturity 2039
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,963
Estimated Fair Value	3,060
Maturity 2042
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,689
Estimated Fair Value	8,156
Maturity 2043
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	14,192
Estimated Fair Value	13,779
Maturity 2044
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	22,132
Estimated Fair Value	21,556
Maturity 2045
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	23,918
Estimated Fair Value	23,005
Maturity 2046
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	37,939
Estimated Fair Value	36,290
Maturity 2047
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	56,376
Estimated Fair Value	54,216
Maturity 2048 [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,851
Estimated Fair Value	$ 15,904

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- Definition

Amortized cost 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 50
-Paragraph 2
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 45
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