Investments Investments (Summary of Unrealized Loss by 12 month Period) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investments Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 117,000	$ 72,970
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(284)	(144)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,649	1,260
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2)	(5)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	118,649	74,230
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(286)	(149)
Corporate Debt Securities [Member]
Investments Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	74,807	57,898
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(212)	(131)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,000	1,260
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(5)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	75,807	59,158
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(213)	(136)
US Treasury and Government [Member]
Investments Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	38,004	15,072
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(62)	(13)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	649	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	38,653	15,072
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(63)	$ (13)
US States and Political Subdivisions Debt Securities [Member]
Investments Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	4,189
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(10)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,189
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (10)