Fair Value Measurement - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Assets, Fair Value Disclosure [Abstract]
Assets, Fair Value Disclosure	$ 50,006	$ 60,618	$ 50,148
Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, Fair Value Disclosure	50,006	60,618	50,148
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, Fair Value Disclosure	0	0	0
Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Assets, Fair Value Disclosure	0	0	0
Money Market Funds [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	50,006	60,618	50,148
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	50,006	60,618	50,148
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	0	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	$ 0	$ 0	$ 0