Marketable Securities - (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 110,061	$ 116,924
Available-for-sale Securities, Fair Value Disclosure	110,055	116,924
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	99,920	113,542
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	99,914	113,549
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis	10,141	3,382
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value	10,141	3,375
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	0	0
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value	0	0
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	0	0
Available-for-sale 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	109,223	116,086
Available-for-sale Securities, Gross Unrealized Gains	14	18
Available-for-sale Securities, Gross Unrealized Losses	20	15
Available-for-sale Securities, Fair Value Disclosure	109,217	116,089
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	57,835	52,638
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	20	15
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	305
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	1
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	838	838
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	3
Available-for-sale Securities, Fair Value Disclosure	838	835
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
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, Aggregate Losses		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, Aggregate Losses		0
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	110,061	116,924
Available-for-sale Securities, Gross Unrealized Gains	14	18
Available-for-sale Securities, Gross Unrealized Losses	20	18
Available-for-sale Securities, Fair Value Disclosure	110,055	116,924
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	57,835	53,473
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	20	18
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	305
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 0	$ 1