Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	$ 757	$ 757
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	757
Increase (decrease) in fair value	0	(324)	$ 27
Balance at the end of the period	757	757
Recurring
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	757	1,081	1,081
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	757	1,081
Warrant exercise		0
Increase (decrease) in fair value	0	(324)
Balance at the end of the period	757	757	$ 1,081
Recurring | Level 2
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	757	757
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	757
Balance at the end of the period	757	757
Recurring | Level 3
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	0	0
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	0
Balance at the end of the period	$ 0	$ 0