Balance Sheet Account Detail Fair Value Measurements (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 77,418,000	$ 31,313,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Business Acquisition, Contingently Issuable Common Stock, Noncurrent
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	83,300,000
Corporate Debt Securities | Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	42,179,000	95,152,000
Business Acquisition, Contingently Issuable Common Stock, Noncurrent	0	0
Corporate Debt Securities | Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Business Acquisition, Contingently Issuable Common Stock, Noncurrent	0	0
Corporate Debt Securities | Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Business Acquisition, Contingently Issuable Common Stock, Noncurrent	49,100,000	60,900,000
Corporate Debt Securities | Fair Value, Measurements, Recurring | Total
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	42,179,000	95,152,000
Business Acquisition, Contingently Issuable Common Stock, Noncurrent	$ 49,100,000	$ 60,900,000