Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of income taxes computed using the federal statutory rate to the taxes reported in consolidated statements of operations
Loss before income taxes	$ 19,566	$ 16,340	$ 19,920
Federal statutory rate	34.00%	34.00%	34.00%
Taxes computed at federal statutory rate	$ (6,652)	$ (5,556)	$ (6,773)
State taxes (net of federal benefit)	(1,016)	(392)	(463)
Warrants	0	(118)	(10)
Nondeductible stock compensation	549	543	48
State Rate Change	(614)	0	0
Michigan NOL benefit	0	0	0
Net operating loss expirations	0	0	655
Write-off of Section 382 limited NOL’s	0	0	67,781
Write-off of Section 383 limited R&D credits	0	0	1,600
Other	56	57	352
Adjustment to prior year filed returns	0	(5,203)	0
Change in valuation allowance	7,677	10,669	(63,190)
Reported income taxes	0	0	$ 0
Deferred tax assets
Net operating loss carryforwards	10,343	13,998
Employee benefits and stock compensation	2,896	2,485
Research and development costs	13,659	4,903
Fixed assets	700	453
Intangible assets	0	(477)
Inventory reserve	1,898	510
Other, net	196	143
Total deferred tax assets	29,692	22,015
Valuation allowance	(29,692)	(22,015)
Net deferred tax assets	$ 0	$ 0