Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Short-term investments in a continuous unrealized loss position, twelve months or longer	$ 0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(83,000)	(320,000)
Gross Unrealized Losses	(76,000)	(2,000)
Gross Unrealized Gains	11,000	12,000
Fair Value	65,428,000	64,806,000
Cost	65,493,000	64,796,000
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	(3,000)	0
Gross Unrealized Gains	5,000	2,000
Fair Value	14,977,000	13,993,000
Cost	14,975,000	13,991,000
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	(68,000)	0
Gross Unrealized Gains	3,000	10,000
Fair Value	43,262,000	36,957,000
Cost	43,327,000	36,947,000
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	0	(2,000)
Gross Unrealized Gains	3,000	0
Fair Value	5,194,000	13,856,000
Cost	5,191,000	13,858,000
Auction Rate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Auction Rate Notes Sold	3,200,000
Gross Unrealized Losses	(64,000)	(505,000)
Gross Unrealized Gains	0	0
Fair Value	1,436,000	4,195,000
Cost	1,500,000	4,700,000
Available-for-sale Securities, Amortized Cost Basis	1,500,000
U.S. Government Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	(5,000)	0
Gross Unrealized Gains	0	0
Fair Value	1,995,000	0
Cost	$ 2,000,000	$ 0