Fair Value Measurement Cash and Cash Equivalents (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Assets, Fair Value Disclosure
Total Assets, Fair Value	$ 22,896	$ 10,057	$ 12,041
Level 1
Assets, Fair Value Disclosure
Total Assets, Fair Value	22,896	10,057	12,041
Level 2
Assets, Fair Value Disclosure
Total Assets, Fair Value	0	0	0
Level 3
Assets, Fair Value Disclosure
Total Assets, Fair Value	0	0	0
Money Market Funds
Assets, Fair Value Disclosure
Cash equivalents	22,896	10,057	12,041
Money Market Funds | Level 1
Assets, Fair Value Disclosure
Cash equivalents	22,896	10,057	12,041
Money Market Funds | Level 2
Assets, Fair Value Disclosure
Cash equivalents	0	0	0
Money Market Funds | Level 3
Assets, Fair Value Disclosure
Cash equivalents	$ 0	$ 0	$ 0