Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Stock options
Outstanding at beginning of year (in shares)	433,389
Granted (in shares)	349,500
Cancelled or forfeited (in shares)	(24,585)
Outstanding at end of year (in shares)	758,304		433,389
Vested and Exercisable to vest at end of year (in shares)	197,643
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 29.05
Granted (in dollars per share)	4.39
Cancelled or forfeited (in dollars per share)	14.35
Outstanding at end of year (in dollars per share)	18.16		$ 29.05
Vested and Exercisable at end of year (in dollars per share)	$ 46.85
Weighted Average Remaining Contractual Term (years)
Outstanding at end of year	8 years 8 months 5 days		7 years 11 months 19 days
Vested and Exercisable at end of year	6 years 4 months 28 days
Aggregate Intrinsic Value
Outstanding at the end of the year	$ 1,318,000
Vested and Exercisable at end of year	2,000
Stock options
Unrecognized stock-based compensation expense
Intrinsic value of options exercised	0	$ 0
Adjusted fair value of options vested	$ 500,000	$ 600,000
Weighted average grant date fair value of options granted (in dollars per share)	$ 3.00	$ 8.80
Unrecognized compensation expense related to unvested stock option awards	$ 2,700,000
Weighted-average amortization period over which cost is expected to be recognized	2 years 2 months 12 days