Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Short Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 65,928	$ 64,796
Gross Unrealized Gains	22	12
Gross Unrealized Losses	0	(2)
Fair Value	65,950	64,806
Short Term Investments [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	36,617	36,947
Gross Unrealized Gains	9	10
Gross Unrealized Losses	0	0
Fair Value	36,626	36,957
Short Term Investments [Member] | Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	16,473	13,991
Gross Unrealized Gains	6	2
Gross Unrealized Losses	0	0
Fair Value	16,479	13,993
Short Term Investments [Member] | Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	12,838	13,858
Gross Unrealized Gains	7	0
Gross Unrealized Losses	0	(2)
Fair Value	12,845	13,856
Long Term Investments [Member] | Auction Rate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,800	4,700
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(68)	(505)
Fair Value	$ 1,732	$ 4,195