Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	$ 1,081	$ 1,081
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	1,081
Increase (decrease) in fair value	(324)	27	$ (5,337)
Balance at the end of the period	757	1,081
Recurring
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	1,081	2,019	2,019
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	1,081	2,019
Warrant exercise		(965)
Increase (decrease) in fair value	(324)	27
Balance at the end of the period	757	1,081	$ 2,019
Recurring | Level 2
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	1,061	1,061
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	1,061
Balance at the end of the period	757	1,061
Recurring | Level 3
Liabilities that are measured at fair value on a recurring basis
Warrant liabilities	20	20
Change in the estimated fair value of warrant liabilities
Balance at the beginning of the period	20
Balance at the end of the period	$ 0	$ 20