Investments - Cost or Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 831,127	$ 653,715
Gross Unrealized Gains	1,922	1,579
Gross Unrealized Losses	(12,611)	(5,960)
Fair Value	820,438	649,334
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		10,000
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		10,000
U.S. government obligations and agencies \| Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	67,435	60,481
Gross Unrealized Gains	241	0
Gross Unrealized Losses	(1,039)	(877)
Fair Value	66,637	59,604
Corporate bonds \| Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	434,887	228,336
Gross Unrealized Gains	714	476
Gross Unrealized Losses	(6,736)	(1,308)
Fair Value	428,865	227,504
Mortgage-backed and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	312,840	221,956
Fair Value	309,597	219,452
Mortgage-backed and asset-backed securities \| Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	312,840	221,956
Gross Unrealized Gains	912	19
Gross Unrealized Losses	(4,155)	(2,523)
Fair Value	309,597	219,452
Municipal bonds \| Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,405	120,883
Gross Unrealized Gains	0	599
Gross Unrealized Losses	(43)	(1,187)
Fair Value	3,362	120,295
Redeemable preferred stock \| Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12,560	12,059
Gross Unrealized Gains	55	485
Gross Unrealized Losses	(638)	(65)
Fair Value	$ 11,977	$ 12,479

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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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

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-Publisher FASB
-Name Accounting Standards Codification
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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