Investments, Summary of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available-for-sale Debt Securities [Abstract]
Fair value	$ 671,973	$ 592,645
Cost or amortized cost	669,128	600,504
Gross unrealized gains	6,477	2,934
Gross unrealized losses	(3,632)	(10,793)
Net unrealized gains (losses)	2,845	(7,859)
Agency Collateralized Mortgage Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	15,773	10,687
Cost or amortized cost	15,567	10,636
Gross unrealized gains	265	145
Gross unrealized losses	(59)	(94)
Net unrealized gains (losses)	206	51
Agency Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	41,283	37,385
Cost or amortized cost	40,486	37,168
Gross unrealized gains	849	371
Gross unrealized losses	(52)	(154)
Net unrealized gains (losses)	797	217
Asset-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	77,307	64,422
Cost or amortized cost	77,890	66,241
Gross unrealized gains	180	14
Gross unrealized losses	(763)	(1,833)
Net unrealized gains (losses)	(583)	(1,819)
Bank Loans [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	11,284	9,750
Cost or amortized cost	11,372	10,208
Gross unrealized gains	38	27
Gross unrealized losses	(126)	(485)
Net unrealized gains (losses)	(88)	(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	5,433	5,423
Cost or amortized cost	5,072	5,095
Gross unrealized gains	433	376
Gross unrealized losses	(72)	(48)
Net unrealized gains (losses)	361	328
Corporate Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	227,529	190,450
Cost or amortized cost	227,017	196,925
Gross unrealized gains	2,110	127
Gross unrealized losses	(1,598)	(6,602)
Net unrealized gains (losses)	512	(6,475)
Mortgage-backed Securities [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	37,984	38,540
Cost or amortized cost	37,699	38,586
Gross unrealized gains	588	377
Gross unrealized losses	(303)	(423)
Net unrealized gains (losses)	285	(46)
Municipal Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	30,357	29,155
Cost or amortized cost	30,056	29,102
Gross unrealized gains	383	239
Gross unrealized losses	(82)	(186)
Net unrealized gains (losses)	301	53
Non-U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	30,879	25,180
Cost or amortized cost	30,810	25,339
Gross unrealized gains	162	6
Gross unrealized losses	(93)	(165)
Net unrealized gains (losses)	69	(159)
U.S. Government Obligations [Member]
Available-for-sale Debt Securities [Abstract]
Fair value	191,309	178,818
Cost or amortized cost	190,324	178,369
Gross unrealized gains	1,469	1,252
Gross unrealized losses	(484)	(803)
Net unrealized gains (losses)	$ 985	$ 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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