Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Document Period End Date	Dec. 31, 2012
Available-for-sale Securities, Failed Auction, Value	$ 346	$ 363
Available-for-sale Securities, Amortized Cost Basis	65,063	70,975
Available-for-sale Securities, Fair Value Disclosure	64,963	70,888
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	57,367	59,469
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	57,390	59,509
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis	7,016	10,587
Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value	7,022	10,599
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis	205	314
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value	205	312
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	475	605
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	346	468
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	64,088	70,475
Available-for-sale Securities, Gross Unrealized Gains	36	60
Available-for-sale Securities, Gross Unrealized Losses	(7)	(10)
Available-for-sale Securities, Fair Value Disclosure	64,117	70,525
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	9,037	7,291
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(7)	(10)
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, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0
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
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	475	500
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	(129)	(137)
Available-for-sale Securities, Fair Value Disclosure	346	363
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	346	363
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(129)	(137)
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	65,063	70,975
Available-for-sale Securities, Gross Unrealized Gains	36	60
Available-for-sale Securities, Gross Unrealized Losses	(136)	(147)
Available-for-sale Securities, Fair Value Disclosure	64,963	70,888
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	9,037	7,291
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(7)	(10)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	346	363
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ (129)	$ (137)