Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Allowance for doubtful accounts	$ 1,578	$ 2,133
Accumulated depreciation, Property, plant and equipment	15,795	16,017
Accumulated depreciation, Rental assets	11,925	12,791
Accumulated amortization, Intangible assets	$ 39,991	$ 33,223
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	96,179,991	81,974,051
Common stock, shares outstanding (in shares)	96,179,991	81,974,051
Series E Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	39,500	10,000
Preferred stock issued (in shares)	37,330	10,000
Preferred stock, shares outstanding (in shares)	37,330	10,000
Preferred stock, liquidation preference per share (in dollars per share)	$ 1,000	$ 1,000