Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Cash equivalents and investments
Gross Unrealized Gains	$ 9		$ 9		$ 4
Gross Unrealized Losses	(4)		(4)		(7)
Total, Amortized Cost	19,193		19,193		26,422
Total, Estimated Fair Value	19,198		19,198		26,419
Other income (expense), net	17	4	33	(21)
Reclassification out of accumulated other comprehensive income (loss)
Cash equivalents and investments
Other income (expense), net			0	0
Short-term investments | U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost	9,101		9,101		2,071
Gross Unrealized Gains	5		5
Investments, Estimated Fair Value	9,106		9,106		2,071
Short-term investments | U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	2,437		2,437		1,454
Investments, Estimated Fair Value	2,437		2,437		1,454
Long-term investments | U.S. treasury notes
Cash equivalents and investments
Investments, Amortized Cost	1,998		1,998		9,116
Gross Unrealized Gains	4		4		3
Gross Unrealized Losses					(2)
Investments, Estimated Fair Value	2,002		2,002		9,117
Long-term investments | U.S. government agency securities
Cash equivalents and investments
Investments, Amortized Cost	5,063		5,063		8,187
Gross Unrealized Gains					1
Gross Unrealized Losses	(4)		(4)		(5)
Investments, Estimated Fair Value	5,059		5,059		8,183
Money market funds
Cash equivalents and investments
Cash equivalents, Estimated Fair Value	357		357		5,356
Investments, Amortized Cost	357		357		5,356
Certificates of deposit | Short-term investments
Cash equivalents and investments
Investments, Amortized Cost	237		237
Investments, Estimated Fair Value	237		237
Certificates of deposit | Long-term investments
Cash equivalents and investments
Investments, Amortized Cost					238
Investments, Estimated Fair Value					$ 238