Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Pre-Tax Amount
December 31, 2017	$ (11,910)
Changes in net unrealized gains on investments	14,200
Reclassification adjustment for realized gains	(181)
September 30, 2018	2,109
Tax (Expense) Benefit
December 31, 2017	2,880
Changes in net unrealized gains on investments	(3,504)
Reclassification adjustment for realized gains	45
September 30, 2018	(579)
Net-of-Tax Amount
December 31, 2017	(9,030)
Changes in net unrealized gains on investments	10,696
Reclassification adjustment for realized gains	136
September 30, 2018	$ 1,530

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Tax (Expense) Benefit [Abstract]

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount before tax of increase (decrease) in accumulated equity from transactions and other events and circumstances from non-owner sources, attributable to parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).

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Amount of tax expense (benefit) allocated to accumulated other comprehensive income (loss) attributable to parent.

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