Investments (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 81,584,000
Unrealized Gains	8,000
Unrealized Losses	(28,000)
Fair Value/Net Carrying Value	81,564,000	$ 0
Total cash equivalents	16,912,000
Total investments	64,652,000
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,485,000
Fair Value/Net Carrying Value	4,485,000
Total cash equivalents	4,485,000
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,481,000
Fair Value/Net Carrying Value	32,481,000
Total cash equivalents	5,999,000
Total investments	26,482,000
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	35,870,000
Unrealized Gains	3,000
Unrealized Losses	(28,000)
Fair Value/Net Carrying Value	35,845,000
Total cash equivalents	1,457,000
Total investments	34,387,000
Municipal bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,748,000
Unrealized Gains	5,000
Fair Value/Net Carrying Value	8,753,000
Total cash equivalents	4,971,000
Total investments	$ 3,783,000