Investments, Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale Debt Securities [Abstract]
Fair value	$ 851,937	$ 795,538
Cost or amortized cost	832,961	783,047
Gross unrealized gains	30,683	16,043
Gross unrealized losses	(11,707)	(3,552)
Net unrealized gains (losses)	18,976	12,491
Agency Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	10,106	12,093
Cost or amortized cost	9,992	11,557
Gross unrealized gains	401	536
Gross unrealized losses	(287)	0
Net unrealized gains (losses)	114	536
Agency Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	98,651	56,280
Cost or amortized cost	95,597	54,286
Gross unrealized gains	3,079	2,005
Gross unrealized losses	(25)	(11)
Net unrealized gains (losses)	3,054	1,994
Asset-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	102,193	106,397
Cost or amortized cost	104,985	107,028
Gross unrealized gains	579	499
Gross unrealized losses	(3,371)	(1,130)
Net unrealized gains (losses)	(2,792)	(631)
Bank Loans [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	8,580	14,568
Cost or amortized cost	9,605	14,932
Gross unrealized gains	0	106
Gross unrealized losses	(1,025)	(470)
Net unrealized gains (losses)	(1,025)	(364)
Certificates of Deposit [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	520	2,835
Cost or amortized cost	520	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	6,034	5,616
Cost or amortized cost	6,167	5,123
Gross unrealized gains	56	493
Gross unrealized losses	(189)	0
Net unrealized gains (losses)	(133)	493
Corporate Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	324,116	281,381
Cost or amortized cost	310,689	274,340
Gross unrealized gains	14,579	7,492
Gross unrealized losses	(1,152)	(451)
Net unrealized gains (losses)	13,427	7,041
Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	43,233	47,463
Cost or amortized cost	47,780	46,685
Gross unrealized gains	1,051	1,047
Gross unrealized losses	(5,598)	(269)
Net unrealized gains (losses)	(4,547)	778
Municipal Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	43,920	36,286
Cost or amortized cost	42,266	35,749
Gross unrealized gains	1,694	684
Gross unrealized losses	(40)	(147)
Net unrealized gains (losses)	1,654	537
Non-U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	29,718	24,179
Cost or amortized cost	28,896	23,889
Gross unrealized gains	822	290
Gross unrealized losses	0	0
Net unrealized gains (losses)	822	290
U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	184,866	208,440
Cost or amortized cost	176,464	206,623
Gross unrealized gains	8,422	2,891
Gross unrealized losses	(20)	(1,074)
Net unrealized gains (losses)	$ 8,402	$ 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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