Common Stock Warrant and Option Exercises and Employee Stock Purchases (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Stock Warrant and Option Exercises and Employee Stock Purchases
Warrant exercises, Shares	1,370	2,968	5,544
Stock option exercises, Shares	0	406	374
Employee stock purchases, Shares	121	28	14
Total, Shares	1,491	3,402	5,932
Warrant exercises	$ 2,000	$ 1,888	$ 7,534
Stock option exercises		584	890
Employee stock purchases	172	74	32
Total, Proceeds	$ 2,172	$ 2,546	$ 8,456