Investments, Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Debt Securities [Abstract]
Fair value	$ 795,538	$ 592,645
Cost or amortized cost	783,047	600,504
Gross unrealized gains	16,043	2,934
Gross unrealized losses	(3,552)	(10,793)
Net unrealized gains (losses)	12,491	(7,859)
Agency Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	12,093	10,687
Cost or amortized cost	11,557	10,636
Gross unrealized gains	536	145
Gross unrealized losses	0	(94)
Net unrealized gains (losses)	536	51
Agency Mortgage Backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	56,280	37,385
Cost or amortized cost	54,286	37,168
Gross unrealized gains	2,005	371
Gross unrealized losses	(11)	(154)
Net unrealized gains (losses)	1,994	217
Asset-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	106,397	64,422
Cost or amortized cost	107,028	66,241
Gross unrealized gains	499	14
Gross unrealized losses	(1,130)	(1,833)
Net unrealized gains (losses)	(631)	(1,819)
Bank Loans [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	14,568	9,750
Cost or amortized cost	14,932	10,208
Gross unrealized gains	106	27
Gross unrealized losses	(470)	(485)
Net unrealized gains (losses)	(364)	(458)
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	5,616	5,423
Cost or amortized cost	5,123	5,095
Gross unrealized gains	493	376
Gross unrealized losses	0	(48)
Net unrealized gains (losses)	493	328
Corporate Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	281,381	190,450
Cost or amortized cost	274,340	196,925
Gross unrealized gains	7,492	127
Gross unrealized losses	(451)	(6,602)
Net unrealized gains (losses)	7,041	(6,475)
Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	47,463	38,540
Cost or amortized cost	46,685	38,586
Gross unrealized gains	1,047	377
Gross unrealized losses	(269)	(423)
Net unrealized gains (losses)	778	(46)
Municipal Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	36,286	29,155
Cost or amortized cost	35,749	29,102
Gross unrealized gains	684	239
Gross unrealized losses	(147)	(186)
Net unrealized gains (losses)	537	53
Non-U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	24,179	25,180
Cost or amortized cost	23,889	25,339
Gross unrealized gains	290	6
Gross unrealized losses	0	(165)
Net unrealized gains (losses)	290	(159)
U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	208,440	178,818
Cost or amortized cost	206,623	178,369
Gross unrealized gains	2,891	1,252
Gross unrealized losses	(1,074)	(803)
Net unrealized gains (losses)	$ 1,817	$ 449

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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