Marketable Securities - (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Failed Auction, Value	$ 308	$ 277
Unrealized Gain (Loss) on Investments	167
Available-for-sale Securities, Amortized Cost Basis	122,767	86,732
Available-for-sale Securities, Fair Value Disclosure	122,643	86,582
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	110,226	81,495
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	110,253	81,533
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis	12,066	4,762
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value	12,082	4,772
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	475	475
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	308	277
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	122,292	86,257
Available-for-sale Securities, Gross Unrealized Gains	44	50
Available-for-sale Securities, Gross Unrealized Losses	1	2
Available-for-sale Securities, Fair Value Disclosure	122,335	86,305
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	15,122	16,448
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	1	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	0
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	475	475
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	167	198
Available-for-sale Securities, Fair Value Disclosure	308	277
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	308	277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	167	198
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	122,767	86,732
Available-for-sale Securities, Gross Unrealized Gains	44	50
Available-for-sale Securities, Gross Unrealized Losses	168	200
Available-for-sale Securities, Fair Value Disclosure	122,643	86,582
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	15,122	16,448
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	1	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	308	277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 167	$ 198