Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Failed Auction, Value	$ 277	$ 346
Available-for-sale Securities, Amortized Cost Basis	86,731	65,063
Available-for-sale Securities, Fair Value Disclosure	86,582	64,963
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	78,909	57,367
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	78,948	57,390
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis	5,811	7,016
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value	5,821	7,022
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis	0	205
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value	0	205
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	2,011	475
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	1,813	346
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	86,257	64,088
Available-for-sale Securities, Gross Unrealized Gains	50	36
Available-for-sale Securities, Gross Unrealized Losses	(2)	(7)
Available-for-sale Securities, Fair Value Disclosure	86,305	64,117
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	16,448	9,037
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(2)	(7)
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
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis		500
Available-for-sale Securities, Gross Unrealized Gains		0
Available-for-sale Securities, Gross Unrealized Losses		0
Available-for-sale Securities, Fair Value Disclosure		500
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	(198)	(129)
Available-for-sale Securities, Fair Value Disclosure	277	346
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	475	346
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(198)	(129)
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	86,732	65,063
Available-for-sale Securities, Gross Unrealized Gains	50	36
Available-for-sale Securities, Gross Unrealized Losses	(200)	(136)
Available-for-sale Securities, Fair Value Disclosure	86,582	64,963
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	16,448	9,037
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(2)	(7)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	475	346
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (198)	$ (129)