Investments - Cost and Fair Value, Net of Credit Loss Allowance, of Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale securities
Amortized cost	$ 779,318
Estimated fair value	751,653
Corporate debt securities
Available-for-sale securities
Amortized cost	460,508	$ 450,295
Gross unrealized gains	1,954	6,289
Gross unrealized losses	23,165	1,704
Estimated fair value	439,297	454,880
Residential mortgage-backed securities
Available-for-sale securities
Amortized cost	124,082	124,337
Gross unrealized gains	3,748	1,056
Gross unrealized losses	413	50
Estimated fair value	127,417	125,343
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	91,355	67,210
Gross unrealized gains	976	479
Gross unrealized losses	3,729	148
Estimated fair value	88,602	67,541
Collateralized debt obligations
Available-for-sale securities
Amortized cost	94,210	78,059
Gross unrealized gains	40	44
Gross unrealized losses	6,635	247
Estimated fair value	87,615	77,856
Other debt securities
Available-for-sale securities
Amortized cost	9,163	5,049
Gross unrealized gains	84	71
Gross unrealized losses	525	39
Estimated fair value	8,722	5,081
Available-for-sale securities
Available-for-sale securities
Amortized cost	779,318	724,950
Gross unrealized gains	6,802	7,939
Gross unrealized losses	34,467	2,188
Estimated fair value	$ 751,653	$ 730,701

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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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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