UNAUDITED QUARTERLY DATA - Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												6 Months Ended		9 Months Ended		12 Months Ended			36 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 38,225	$ 37,646	$ 34,406	$ 33,522	$ 42,125	$ 33,592	$ 31,532	$ 25,259	$ 31,779	$ 26,301	$ 21,787	$ 21,569	$ 56,791	$ 43,356	$ 90,383	$ 69,657	$ 143,799	$ 132,508	$ 101,436
Gross profit	8,987	9,779	9,243	10,110	10,478	9,845	9,172	6,181	5,977	6,342	6,445	6,297	15,353	12,742	25,198	19,084	38,119	35,676	25,061
Operating (loss) income	(10,143)	(3,892)	(10,200)	(5,921)	(1,002)	(2,566)	(3,905)	(1,750)	(2,401)	(459)	109	(1,383)	(5,655)	(1,274)	(8,221)	(1,733)	(30,156)	(9,223)	(4,134)
Net income (loss)	(10,541)	(4,510)	(10,657)	(6,320)	(1,696)	(3,223)	(4,194)	(2,171)	(2,938)	(925)	(232)	(3,370)	(6,365)	(3,602)	(9,588)	(4,527)	(32,028)	(11,284)	(7,465)	$ (50,800)
Cumulative preferred dividends	0	(334)	0	(334)	0	(334)	0	(334)	0	(334)	0	(334)	(334)	(334)	(668)	(668)	(668)	(668)	(668)
Net (loss) income applicable to common shares	$ (10,541)	$ (4,844)	$ (10,657)	$ (6,654)	$ (1,696)	$ (3,557)	$ (4,194)	$ (2,505)	$ (2,938)	$ (1,259)	$ (232)	$ (3,704)	$ (6,699)	$ (3,936)	$ (10,256)	$ (5,195)	$ (32,696)	$ (11,952)	$ (8,133)
Net earnings (loss) per common share - basic (in USD per share)	$ (0.18)	$ (0.08)	$ (0.18)	$ (0.11)	$ (0.03)	$ (0.07)	$ (0.08)	$ (0.05)	$ (0.07)	$ (0.03)	$ (0.01)	$ (0.10)	$ (0.13)	$ (0.10)	$ (0.20)	$ (0.13)	$ (0.54)	$ (0.23)	$ (0.20)
Net earnings (loss) per common share - diluted (in USD per share)	$ (0.18)	$ (0.08)	$ (0.18)	$ (0.11)	$ (0.03)	$ (0.07)	$ (0.08)	$ (0.05)	$ (0.07)	$ (0.03)	$ (0.01)	$ (0.10)	$ (0.13)	$ (0.10)	$ (0.20)	$ (0.13)	$ (0.54)	$ (0.23)	$ (0.20)
Weighted average number of common shares outstanding - basic (in shares)	60,065,978	60,065,053	60,059,936	60,053,912	54,064,750	53,637,085	52,150,106	47,573,364	40,331,993	40,327,697	40,308,934	38,488,005	49,861,735	39,398,469	51,101,813	39,703,690	60,061,243	51,840,518	39,860,335
Weighted average number of common shares outstanding - diluted (in shares)	60,065,978	60,065,053	60,059,936	60,053,912	54,064,750	53,637,085	52,150,106	47,573,364	40,331,993	40,327,697	40,308,934	38,488,005	49,861,735	39,398,469	51,101,813	39,703,690	60,061,243	51,840,518	39,860,335