Warrants - Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding at beginning of period (in shares)	979,869	913,434
Issued (in shares)	0	489,475
Exercised (in shares)	(75,399)	(410,824)
Expired (in shares)	0	(12,216)
Outstanding at end of period (in shares)	904,470	979,869
Exercisable at end of period (in shares)	904,470
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 6.36	$ 3.54
Issued (in dollars per share)	0.00	2.20
Exercised (in shares)	19.46	1.73
Expired ( in dollars per share)	0.00	22.50
Outstanding at end of period (in dollars per share)	5.27	6.36
Exercisable at end of period (in dollars per share)	5.27
Range of Exercise Prices
Issued (in dollars per share)	0.00	2.20
Expired (in dollars per share)	$ 0.00	22.50
Equity classified as warrants (in shares)	21,920
Minimum
Range of Exercise Prices
Outstanding at beginning of period (in dollars per share)	$ 6.25	6.25
Exercised (in dollars per share)	13.25	0.05
Outstanding at end of period (in dollars per share)	2.20	6.25
Exercisable (in dollars per share)	2.20
Maximum
Range of Exercise Prices
Outstanding at beginning of period (in dollars per share)	52.00	52.00
Exercised (in dollars per share)	21.00	3.00
Outstanding at end of period (in dollars per share)	21.00	$ 52.00
Exercisable (in dollars per share)	$ 21.00