Investments - Cost and Fair Value of Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale securities
Amortized cost	$ 676,336
Estimated fair value	680,633
U.S. Treasury
Available-for-sale securities
Amortized cost		$ 208,610
Gross unrealized gains		18
Gross unrealized losses		216
Estimated fair value		208,412
States & political subdivisions
Available-for-sale securities
Amortized cost		157,003
Gross unrealized gains		2,020
Gross unrealized losses		0
Estimated fair value		159,023
Corporate debt securities
Available-for-sale securities
Amortized cost	431,800	259,362
Gross unrealized gains	4,437	139
Gross unrealized losses	2,031	9,554
Estimated fair value	434,206	249,947
Residential mortgage-backed securities
Available-for-sale securities
Amortized cost	106,401	4,603
Gross unrealized gains	889	38
Gross unrealized losses	55	32
Estimated fair value	107,235	4,609
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	61,940	47,022
Gross unrealized gains	1,263	80
Gross unrealized losses	21	587
Estimated fair value	63,182	46,515
Collateralized debt obligations
Available-for-sale securities
Amortized cost	71,087	65,039
Gross unrealized gains	20	30
Gross unrealized losses	289	830
Estimated fair value	70,818	64,239
Other debt securities
Available-for-sale securities
Amortized cost	5,108	15,756
Gross unrealized gains	92	33
Gross unrealized losses	8	11
Estimated fair value	5,192	15,778
Available-for-sale securities
Available-for-sale securities
Amortized cost	676,336	757,395
Gross unrealized gains	6,701	2,358
Gross unrealized losses	2,404	11,230
Estimated fair value	$ 680,633	$ 748,523

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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