Investments - Cost and Fair Value, Net of Credit Loss Allowance, of Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available-for-sale securities
Amortized cost	$ 792,470
Estimated fair value	804,825
Corporate debt securities
Available-for-sale securities
Amortized cost	461,398	$ 450,295
Gross unrealized gains	14,508	6,289
Gross unrealized losses	6,251	1,704
Estimated fair value	469,655	454,880
Residential mortgage-backed securities
Available-for-sale securities
Amortized cost	115,631	124,337
Gross unrealized gains	3,970	1,056
Gross unrealized losses	2	50
Estimated fair value	119,599	125,343
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	104,403	67,210
Gross unrealized gains	3,390	479
Gross unrealized losses	1,251	148
Estimated fair value	106,542	67,541
Collateralized debt obligations
Available-for-sale securities
Amortized cost	98,603	78,059
Gross unrealized gains	281	44
Gross unrealized losses	2,596	247
Estimated fair value	96,288	77,856
Other debt securities
Available-for-sale securities
Amortized cost	12,435	5,049
Gross unrealized gains	355	71
Gross unrealized losses	49	39
Estimated fair value	12,741	5,081
Available-for-sale securities
Available-for-sale securities
Amortized cost	792,470	724,950
Gross unrealized gains	22,504	7,939
Gross unrealized losses	10,149	2,188
Estimated fair value	$ 804,825	$ 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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Amortized cost 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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