Share-Based Compensation - Exercise Prices (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding at end of year (in shares)	1,608,646	1,412,940
Wgtd. Avg. Remaining Contractual Life	8 years 29 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 6.20	$ 7.13
Options exercisable (in shares)	705,594
Wgtd. Avg. Exercise Price (usd per share)	$ 10.34
$0.00-$2.49
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	0
Exercise price range, upper range limit	$ 2.49
Outstanding at end of year (in shares)	285,503
Wgtd. Avg. Remaining Contractual Life	9 years 5 months 23 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 1.97
Options exercisable (in shares)	22,150
Wgtd. Avg. Exercise Price (usd per share)	$ 2.37
$2.50-$3.49
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	2.50
Exercise price range, upper range limit	$ 3.49
Outstanding at end of year (in shares)	878,833
Wgtd. Avg. Remaining Contractual Life	8 years 8 months 27 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 3.17
Options exercisable (in shares)	362,973
Wgtd. Avg. Exercise Price (usd per share)	$ 3.17
$3.50-$4.99
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	3.50
Exercise price range, upper range limit	$ 4.99
Outstanding at end of year (in shares)	206,769
Wgtd. Avg. Remaining Contractual Life	8 years 4 months 17 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 4.26
Options exercisable (in shares)	82,930
Wgtd. Avg. Exercise Price (usd per share)	$ 4.23
$15.00-$30.32
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	15.00
Exercise price range, upper range limit	$ 30.32
Outstanding at end of year (in shares)	237,541
Wgtd. Avg. Remaining Contractual Life	3 years 8 months 16 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 24.18
Options exercisable (in shares)	237,541
Wgtd. Avg. Exercise Price (usd per share)	$ 24.18