Investments, Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available-for-sale Debt Securities [Abstract]
Fair value	$ 812,001	$ 795,538
Cost or amortized cost	800,519	783,047
Gross unrealized gains	29,515	16,043
Gross unrealized losses	(18,033)	(3,552)
Net unrealized gains (losses)	11,482	12,491
Agency Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	11,054	12,093
Cost or amortized cost	10,869	11,557
Gross unrealized gains	428	536
Gross unrealized losses	(243)	0
Net unrealized gains (losses)	185	536
Agency Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	91,512	56,280
Cost or amortized cost	88,344	54,286
Gross unrealized gains	3,192	2,005
Gross unrealized losses	(24)	(11)
Net unrealized gains (losses)	3,168	1,994
Asset-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	99,830	106,397
Cost or amortized cost	104,961	107,028
Gross unrealized gains	597	499
Gross unrealized losses	(5,728)	(1,130)
Net unrealized gains (losses)	(5,131)	(631)
Bank Loans [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	8,121	14,568
Cost or amortized cost	9,609	14,932
Gross unrealized gains	0	106
Gross unrealized losses	(1,488)	(470)
Net unrealized gains (losses)	(1,488)	(364)
Certificates of Deposit [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	2,835	2,835
Cost or amortized cost	2,835	2,835
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Net unrealized gains (losses)	0	0
Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	6,749	5,616
Cost or amortized cost	7,046	5,123
Gross unrealized gains	40	493
Gross unrealized losses	(337)	0
Net unrealized gains (losses)	(297)	493
Corporate Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	295,894	281,381
Cost or amortized cost	284,676	274,340
Gross unrealized gains	13,318	7,492
Gross unrealized losses	(2,100)	(451)
Net unrealized gains (losses)	11,218	7,041
Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	45,502	47,463
Cost or amortized cost	53,106	46,685
Gross unrealized gains	478	1,047
Gross unrealized losses	(8,082)	(269)
Net unrealized gains (losses)	(7,604)	778
Municipal Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	38,359	36,286
Cost or amortized cost	36,967	35,749
Gross unrealized gains	1,421	684
Gross unrealized losses	(29)	(147)
Net unrealized gains (losses)	1,392	537
Non-U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	30,210	24,179
Cost or amortized cost	29,312	23,889
Gross unrealized gains	900	290
Gross unrealized losses	(2)	0
Net unrealized gains (losses)	898	290
U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	181,935	208,440
Cost or amortized cost	172,794	206,623
Gross unrealized gains	9,141	2,891
Gross unrealized losses	0	(1,074)
Net unrealized gains (losses)	$ 9,141	$ 1,817

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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