Investments (Summary of Gross Unrealized Loss Position) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	$ 309,764	$ 284,888
Unrealized Losses 12 months or less	(12,496)	(3,162)
Fair Value Longer than 12 months	169,544	17,224
Unrealized Losses Longer than 12 months	(7,289)	(254)
Fair Value Total	479,308	302,112
Unrealized Losses Total	(19,785)	(3,416)
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	1,148
Unrealized Losses 12 months or less	(2,615)
Fair Value Longer than 12 months
Unrealized Losses Longer than 12 months
Fair Value Total	1,148
Unrealized Losses Total	(2,615)
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	277,635	276,513
Unrealized Losses 12 months or less	(6,182)	(1,658)
Fair Value Longer than 12 months	165,069	17,224
Unrealized Losses Longer than 12 months	(2,482)	(254)
Fair Value Total	442,704	293,737
Unrealized Losses Total	(8,664)	(1,912)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	30,981	8,375
Unrealized Losses 12 months or less	(3,699)	(1,504)
Fair Value Longer than 12 months	4,475
Unrealized Losses Longer than 12 months	(4,807)
Fair Value Total	35,456	8,375
Unrealized Losses Total	(8,506)	(1,504)
U.S. Treasury securities and obligations of U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	18,902	28,825
Unrealized Losses 12 months or less	(181)	(145)
Fair Value Longer than 12 months	28,201	1,997
Unrealized Losses Longer than 12 months	(327)	(3)
Fair Value Total	47,103	30,822
Unrealized Losses Total	(508)	(148)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	117,450	176,061
Unrealized Losses 12 months or less	(907)	(736)
Fair Value Longer than 12 months	100,060	2,378
Unrealized Losses Longer than 12 months	(695)	(6)
Fair Value Total	217,510	178,439
Unrealized Losses Total	(1,602)	(742)
Collateralized Corporate Bank Loans [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	120,410	30,008
Unrealized Losses 12 months or less	(4,938)	(280)
Fair Value Longer than 12 months	4,931	2,517
Unrealized Losses Longer than 12 months	(332)	(21)
Fair Value Total	125,341	32,525
Unrealized Losses Total	(5,270)	(301)
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	14,281	35,200
Unrealized Losses 12 months or less	(96)	(370)
Fair Value Longer than 12 months	25,891	8,917
Unrealized Losses Longer than 12 months	(742)	(135)
Fair Value Total	40,172	44,117
Unrealized Losses Total	(838)	(505)
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 months or less	6,592	6,419
Unrealized Losses 12 months or less	(60)	(127)
Fair Value Longer than 12 months	5,986	1,415
Unrealized Losses Longer than 12 months	(386)	(89)
Fair Value Total	12,578	7,834
Unrealized Losses Total	$ (446)	$ (216)