Investments, Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale Debt Securities [Abstract]
Fair value	$ 757,841	$ 592,645
Cost or amortized cost	744,762	600,504
Gross unrealized gains	16,007	2,934
Gross unrealized losses	(2,928)	(10,793)
Net unrealized gains (losses)	13,079	(7,859)
Agency Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	14,426	10,687
Cost or amortized cost	13,911	10,636
Gross unrealized gains	518	145
Gross unrealized losses	(3)	(94)
Net unrealized gains (losses)	515	51
Agency Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	51,246	37,385
Cost or amortized cost	49,567	37,168
Gross unrealized gains	1,691	371
Gross unrealized losses	(12)	(154)
Net unrealized gains (losses)	1,679	217
Asset-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	99,295	64,422
Cost or amortized cost	99,834	66,241
Gross unrealized gains	580	14
Gross unrealized losses	(1,119)	(1,833)
Net unrealized gains (losses)	(539)	(1,819)
Bank Loans [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	14,625	9,750
Cost or amortized cost	14,871	10,208
Gross unrealized gains	54	27
Gross unrealized losses	(300)	(485)
Net unrealized gains (losses)	(246)	(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	5,718	5,423
Cost or amortized cost	5,234	5,095
Gross unrealized gains	571	376
Gross unrealized losses	(87)	(48)
Net unrealized gains (losses)	484	328
Corporate Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	267,223	190,450
Cost or amortized cost	261,191	196,925
Gross unrealized gains	6,858	127
Gross unrealized losses	(826)	(6,602)
Net unrealized gains (losses)	6,032	(6,475)
Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	47,381	38,540
Cost or amortized cost	46,235	38,586
Gross unrealized gains	1,290	377
Gross unrealized losses	(144)	(423)
Net unrealized gains (losses)	1,146	(46)
Municipal Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	32,986	29,155
Cost or amortized cost	32,280	29,102
Gross unrealized gains	755	239
Gross unrealized losses	(49)	(186)
Net unrealized gains (losses)	706	53
Non-U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	24,068	25,180
Cost or amortized cost	23,705	25,339
Gross unrealized gains	364	6
Gross unrealized losses	(1)	(165)
Net unrealized gains (losses)	363	(159)
U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	198,038	178,818
Cost or amortized cost	195,099	178,369
Gross unrealized gains	3,326	1,252
Gross unrealized losses	(387)	(803)
Net unrealized gains (losses)	$ 2,939	$ 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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