Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Series D Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balances at Dec. 31, 2018		$ 3,059	$ 40,685	$ 74,575
Beginning balances, Shares at Dec. 31, 2018		388,558	3,088,444	4,499,921
Beginning balances at Dec. 31, 2018	$ (131,824)					$ 1	$ 30,150	$ (161,995)	$ 20
Beginning balances, Shares at Dec. 31, 2018						656,654
Unrealized loss on marketable securities	7								7
Foreign currency translation adjustment	(12)								(12)
Issuance of Series A preferred stock for cashless warrant exercise		2,652
Issuance of Series D convertible preferred stock for cash, net of issuance costs of $274					$ 38,226
Issuance of Series D convertible preferred stock for cash, net of issuance costs of $274, Shares					2,309,959
Issuance of Series D convertible preferred stock for 2018 Convertible Notes and 2019 Convertible Notes					$ 68,476
Issuance of Series D convertible preferred stock for 2018 Convertible Notes and 2019 Convertible Notes, Shares					4,108,478
Stock option exercises	57						57
Stock option exercises, Shares						8,469
Stock-based compensation	1,362						1,362
Stock-based compensation, Shares						6,837
Net loss	(45,040)							(45,040)
Ending balances at Jun. 30, 2019		$ 3,059	$ 40,685	$ 74,575	$ 106,702
Ending balances, shares at Jun. 30, 2019		391,210	3,088,444	4,499,921	6,418,437
Ending balances at Jun. 30, 2019	(175,450)					$ 1	31,569	(207,035)	15
Ending balances, shares at Jun. 30, 2019						671,960
Beginning balances at Mar. 31, 2019		$ 3,059	$ 40,685	$ 74,575
Beginning balances, Shares at Mar. 31, 2019		391,210	3,088,444	4,499,921
Beginning balances at Mar. 31, 2019	(145,973)					$ 1	30,709	(176,690)	7
Beginning balances, Shares at Mar. 31, 2019						656,654
Unrealized loss on marketable securities	6								6
Foreign currency translation adjustment	2								2
Issuance of Series D convertible preferred stock for cash, net of issuance costs of $274					$ 38,226
Issuance of Series D convertible preferred stock for cash, net of issuance costs of $274, Shares					2,309,959
Issuance of Series D convertible preferred stock for 2018 Convertible Notes and 2019 Convertible Notes					$ 68,476
Issuance of Series D convertible preferred stock for 2018 Convertible Notes and 2019 Convertible Notes, Shares					4,108,478
Stock option exercises	57						57
Stock option exercises, Shares						8,469
Stock-based compensation	803						803
Stock-based compensation, Shares						6,837
Net loss	(30,345)							(30,345)
Ending balances at Jun. 30, 2019		$ 3,059	$ 40,685	$ 74,575	$ 106,702
Ending balances, shares at Jun. 30, 2019		391,210	3,088,444	4,499,921	6,418,437
Ending balances at Jun. 30, 2019	(175,450)					$ 1	31,569	(207,035)	15
Ending balances, shares at Jun. 30, 2019						671,960
Beginning balances at Dec. 31, 2019		$ 3,059	$ 40,685	$ 74,575	$ 135,039
Beginning balances, Shares at Dec. 31, 2019		391,210	3,088,444	4,499,921	8,200,297
Beginning balances at Dec. 31, 2019	(225,811)					$ 1	33,252	(259,034)	(30)
Beginning balances, Shares at Dec. 31, 2019						695,902
Unrealized loss on marketable securities	(41)								(41)
Foreign currency translation adjustment	69								69
Issuance of Series D convertible preferred stock for the Biotronik Asset Purchase					$ 5,000
Issuance of Series D convertible preferred stock for the Biotronik Asset Purchase, Shares					273,070
Issuance of Series D convertible preferred stock for the contingent consideration related to the Rhythm Xience Acquisition					$ 2,197
Issuance of Series D convertible preferred stock for the contingent consideration related to the Rhythm Xience Acquisition, Shares					119,993
Stock option exercises	205						205
Stock option exercises, Shares						64,562
Stock-based compensation	2,898						2,898
Stock-based compensation, Shares						14,939
Net loss	(41,291)							(41,291)
Ending balances at Jun. 30, 2020		$ 3,059	$ 40,685	$ 74,575	$ 142,236
Ending balances, shares at Jun. 30, 2020		391,210	3,088,444	4,499,921	8,593,360
Ending balances at Jun. 30, 2020	(263,971)					$ 1	36,355	(300,325)	(2)
Ending balances, shares at Jun. 30, 2020						775,403
Beginning balances at Mar. 31, 2020		$ 3,059	$ 40,685	$ 74,575	$ 142,236
Beginning balances, Shares at Mar. 31, 2020		391,210	3,088,444	4,499,921	8,593,360
Beginning balances at Mar. 31, 2020	(242,222)					$ 1	34,993	(277,132)	(84)
Beginning balances, Shares at Mar. 31, 2020						710,841
Unrealized loss on marketable securities	(14)								(14)
Foreign currency translation adjustment	96								96
Stock option exercises	205						205
Stock option exercises, Shares						64,562
Stock-based compensation	1,157						1,157
Net loss	(23,193)							(23,193)
Ending balances at Jun. 30, 2020		$ 3,059	$ 40,685	$ 74,575	$ 142,236
Ending balances, shares at Jun. 30, 2020		391,210	3,088,444	4,499,921	8,593,360
Ending balances at Jun. 30, 2020	$ (263,971)					$ 1	$ 36,355	$ (300,325)	$ (2)
Ending balances, shares at Jun. 30, 2020						775,403