Investments, Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale Debt Securities [Abstract]
Fair value	$ 737,148	$ 592,645
Cost or amortized cost	726,053	600,504
Gross unrealized gains	13,175	2,934
Gross unrealized losses	(2,080)	(10,793)
Net unrealized gains (losses)	11,095	(7,859)
Agency Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	15,730	10,687
Cost or amortized cost	15,384	10,636
Gross unrealized gains	352	145
Gross unrealized losses	(6)	(94)
Net unrealized gains (losses)	346	51
Agency Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	41,031	37,385
Cost or amortized cost	39,609	37,168
Gross unrealized gains	1,438	371
Gross unrealized losses	(16)	(154)
Net unrealized gains (losses)	1,422	217
Asset-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	94,880	64,422
Cost or amortized cost	94,847	66,241
Gross unrealized gains	539	14
Gross unrealized losses	(506)	(1,833)
Net unrealized gains (losses)	33	(1,819)
Bank Loans [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	16,074	9,750
Cost or amortized cost	16,279	10,208
Gross unrealized gains	60	27
Gross unrealized losses	(265)	(485)
Net unrealized gains (losses)	(205)	(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	6,165	5,423
Cost or amortized cost	5,686	5,095
Gross unrealized gains	549	376
Gross unrealized losses	(70)	(48)
Net unrealized gains (losses)	479	328
Corporate Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	256,318	190,450
Cost or amortized cost	251,977	196,925
Gross unrealized gains	5,185	127
Gross unrealized losses	(844)	(6,602)
Net unrealized gains (losses)	4,341	(6,475)
Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	42,506	38,540
Cost or amortized cost	41,706	38,586
Gross unrealized gains	946	377
Gross unrealized losses	(146)	(423)
Net unrealized gains (losses)	800	(46)
Municipal Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	32,834	29,155
Cost or amortized cost	32,177	29,102
Gross unrealized gains	688	239
Gross unrealized losses	(31)	(186)
Net unrealized gains (losses)	657	53
Non-U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	31,378	25,180
Cost or amortized cost	31,064	25,339
Gross unrealized gains	326	6
Gross unrealized losses	(12)	(165)
Net unrealized gains (losses)	314	(159)
U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	197,397	178,818
Cost or amortized cost	194,489	178,369
Gross unrealized gains	3,092	1,252
Gross unrealized losses	(184)	(803)
Net unrealized gains (losses)	$ 2,908	$ 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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