Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		$ 116,924	$ 113,838
Available-for-sale Securities, Fair Value Disclosure		116,924	113,871
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis		113,542	107,151
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value		113,549	107,177
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis		3,382	6,687
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value		3,375	6,694
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis		0	0
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value		0	0
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis		0	0
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value		0	0
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		116,086	113,838
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		18	37
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(15)	(4)
Available-for-sale Securities, Fair Value Disclosure		116,089	113,871
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 52,638	26,698
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(15)	(4)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	305	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	0
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	835
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)
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 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		116,924	113,838
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		18	37
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(18)	(4)
Available-for-sale Securities, Fair Value Disclosure		116,924	$ 113,871
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	53,473	26,698
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(18)	(4)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	305	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (1)	$ 0