Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income
Balance (in shares) at Dec. 31, 2017		199,282
Balance at Dec. 31, 2017	$ 178,848	$ 199		$ 621,261	$ (447,640)	$ 5,028
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,834			1,834
Exercise of stock options and warrants (in shares)		1,038
Exercise of stock options and warrants	2,228	$ 1		2,227
Award of restricted stock units (in shares)		367
Return of common stock to pay withholding taxes on restricted stock (in shares)			174
Cancellation of treasury stock (in shares)			(174)
Cumulative effect of change in accounting principle	11				11
Other comprehensive (loss) income	2,308					2,308
Issuance of common stock and warrants, net of issuance costs	11			11
Issuance of common stock related to sale of SurgiBot assets (in shares)		1,286
Issuance of common stock related to sale of SurgiBot assets	3,000	$ 1		2,999
Net loss	(882)				(882)
Balance (in shares) at Mar. 31, 2018		201,973
Balance at Mar. 31, 2018	187,358	$ 201		628,332	(448,511)	7,336
Balance (in shares) at Dec. 31, 2017		199,282
Balance at Dec. 31, 2017	178,848	$ 199		621,261	(447,640)	5,028
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(35,130)
Balance (in shares) at Jun. 30, 2018		207,712
Balance at Jun. 30, 2018	165,718	$ 207		645,332	(482,759)	2,938
Balance (in shares) at Mar. 31, 2018		201,973
Balance at Mar. 31, 2018	187,358	$ 201		628,332	(448,511)	7,336
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,370			2,370
Exercise of stock options and warrants (in shares)		5,735
Exercise of stock options and warrants	14,645	$ 6		14,639
Award of restricted stock units (in shares)		4
Return of common stock to pay withholding taxes on restricted stock (in shares)			2
Cancellation of treasury stock (in shares)			(2)
Other comprehensive (loss) income	(4,398)					(4,398)
Issuance of common stock and warrants, net of issuance costs	(9)			(9)
Net loss	(34,248)				(34,248)
Balance (in shares) at Jun. 30, 2018		207,712
Balance at Jun. 30, 2018	165,718	$ 207		645,332	(482,759)	2,938
Balance (in shares) at Dec. 31, 2018		216,346
Balance at Dec. 31, 2018	168,521	$ 216		676,373	(509,406)	1,338
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,981			2,981
Exercise of stock options and warrants (in shares)		159
Exercise of stock options and warrants	236	$ 0		236
Award of restricted stock units (in shares)		613
Award of restricted stock units	1	$ 1
Return of common stock to pay withholding taxes on restricted stock (in shares)			194
Return of common stock to pay withholding taxes on restricted stock	(499)			(499)
Cancellation of treasury stock (in shares)			(194)
Cumulative effect of change in accounting principle	0			(7)	7
Other comprehensive (loss) income	(1,949)					(1,949)
Net loss	(22,525)				(22,525)
Balance (in shares) at Mar. 31, 2019		217,118
Balance at Mar. 31, 2019	146,766	$ 217		679,084	(531,924)	(611)
Balance (in shares) at Dec. 31, 2018		216,346
Balance at Dec. 31, 2018	168,521	$ 216		676,373	(509,406)	1,338
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(42,696)
Balance (in shares) at Jun. 30, 2019		217,625
Balance at Jun. 30, 2019	131,487	$ 217		682,736	(552,095)	629
Balance (in shares) at Mar. 31, 2019		217,118
Balance at Mar. 31, 2019	146,766	$ 217		679,084	(531,924)	(611)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,355			3,355
Exercise of stock options and warrants (in shares)		324
Exercise of stock options and warrants	297			297
Award of restricted stock units (in shares)		183
Award of restricted stock units	0
Other comprehensive (loss) income	1,240					1,240
Net loss	(20,171)				(20,171)
Balance (in shares) at Jun. 30, 2019		217,625
Balance at Jun. 30, 2019	$ 131,487	$ 217		$ 682,736	$ (552,095)	$ 629