Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock 0.00001 Par Value [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ 100,943		$ 538,088	$ (437,145)
Beginning balance, shares at Dec. 31, 2017		23,643,189
Net loss	(6,842)			(6,842)
Stock compensation expense	1,136		1,136
Vesting of restricted stock units	(504)		(504)
Vesting of restricted stock units, shares		239,064
Ending balance at Mar. 31, 2018	94,733		538,720	(443,987)
Ending balance, shares at Mar. 31, 2018		23,882,253
Beginning balance at Dec. 31, 2017	100,943		538,088	(437,145)
Beginning balance, shares at Dec. 31, 2017		23,643,189
Net loss	(13,800)
Ending balance at Jun. 30, 2018	88,925		539,870	(450,945)
Ending balance, shares at Jun. 30, 2018		23,940,315
Beginning balance at Mar. 31, 2018	94,733		538,720	(443,987)
Beginning balance, shares at Mar. 31, 2018		23,882,253
Net loss	(6,958)			(6,958)
Stock compensation expense	1,150		1,150
Issuance of restricted stock, shares		58,062
Ending balance at Jun. 30, 2018	88,925		539,870	(450,945)
Ending balance, shares at Jun. 30, 2018		23,940,315
Beginning balance at Dec. 31, 2018	70,254		541,839	(471,585)
Beginning balance, shares at Dec. 31, 2018		23,973,517
Net loss	(6,002)			(6,002)
Stock compensation expense	878		878
Vesting of restricted stock units	(454)		(454)
Vesting of restricted stock units, shares		273,290
Ending balance at Mar. 31, 2019	64,676		542,263	(477,587)
Ending balance, shares at Mar. 31, 2019		24,246,807
Beginning balance at Dec. 31, 2018	70,254		541,839	(471,585)
Beginning balance, shares at Dec. 31, 2018		23,973,517
Net loss	(11,320)
Ending balance at Jun. 30, 2019	60,344		543,249	(482,905)
Ending balance, shares at Jun. 30, 2019		24,300,264
Beginning balance at Mar. 31, 2019	64,676		542,263	(477,587)
Beginning balance, shares at Mar. 31, 2019		24,246,807
Net loss	(5,318)			(5,318)
Stock compensation expense	996		996
Issuance of restricted stock, shares		50,328
Vesting of restricted stock units	(10)		(10)
Vesting of restricted stock units, shares		3,129
Ending balance at Jun. 30, 2019	$ 60,344		$ 543,249	$ (482,905)
Ending balance, shares at Jun. 30, 2019		24,300,264