Significant Accounting Policies Investments (Details) (USD $)									12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Corporate Debt Securities [Member]	Dec. 31, 2011 Corporate Debt Securities [Member]	Dec. 31, 2012 Commercial Paper [Member]	Dec. 31, 2011 Commercial Paper [Member]	Dec. 31, 2012 U.S. Agencies [Member]	Dec. 31, 2011 U.S. Agencies [Member]	Dec. 31, 2012 Short-term Investments [Member]	Dec. 31, 2012 Municipal Securities [Member]	Dec. 31, 2011 Municipal Securities [Member]	Dec. 31, 2012 Certificates of Deposit [Member]	Dec. 31, 2011 Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Accumulated other comprehensive loss	$ (532,000)	$ (887,000)
Cost	76,606,000	77,726,000	26,575,000	33,723,000	18,464,000	4,991,000		4,528,000		12,520,000	11,413,000	19,047,000	23,071,000
Gross Gains
Gross Losses	(257,000)	(461,000)	(139,000)	(327,000)	(2,000)	(2,000)		(17,000)		(116,000)	(115,000)
Fair Value	76,349,000	77,265,000	26,436,000	33,396,000	18,462,000	4,989,000		4,511,000		12,404,000	11,298,000	19,047,000	23,071,000
Short-term investments in a continuous unrealized loss position, twelve months or longer									8,200,000
Temporary impairment of these securities to accumulated other comprehensive income Net of tax									163,000
Temporary impairment of these securities to accumulated other comprehensive income pre tax									$ 257,000