Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Beginning Balance at Dec. 31, 2016	$ 33	$ 367,851	$ (198,974)	$ (468)	$ 168,442
Beginning Balance, Shares at Dec. 31, 2016	33,342
Issuance of common stock under equity incentive plans	$ 2	2,387			2,389
Issuance of common stock under equity incentive plans, Shares	1,112
Issuance of common stock under employee stock purchase plan		2,110			2,110
Issuance of common stock under employee stock purchase plan, Shares	132
Share-based employee compensation expense		14,615			14,615
Other comprehensive income (loss)				502	502
Net loss			(26,892)		(26,892)
Ending Balance at Dec. 31, 2017	$ 35	386,963	(225,866)	34	161,166
Ending Balance, Shares at Dec. 31, 2017	34,586
Issuance of common stock through public offering	$ 3	82,870			82,873
Issuance of common stock through public offering, Shares	2,875
Issuance of common stock for settlement of contingent consideration		6,279			6,279
Issuance of common stock for settlement of contingent consideration, Shares	232
Issuance of common stock under equity incentive plans	$ 1	1,554			1,555
Issuance of common stock under equity incentive plans, Shares	781
Issuance of common stock under employee stock purchase plan		2,383			2,383
Issuance of common stock under employee stock purchase plan, Shares	130
Share-based employee compensation expense		16,495			16,495
Other comprehensive income (loss)				(233)	(233)
Net loss			(21,137)		(21,137)
Ending Balance at Dec. 31, 2018	$ 39	496,544	(247,003)	(199)	249,381
Ending Balance, Shares at Dec. 31, 2018	38,604
Issuance of common stock for SentreHEART acquisition	$ 1	20,306			20,307
Issuance of common stock for SentreHEART acquisition, Shares	699
Issuance of common stock under equity incentive plans		(7,831)			(7,831)
Issuance of common stock under equity incentive plans, Shares	248
Issuance of common stock under employee stock purchase plan		2,662			2,662
Issuance of common stock under employee stock purchase plan, Shares	104
Share-based employee compensation expense		17,977			17,977
Other comprehensive income (loss)				41	41
Net loss			(35,194)		(35,194)
Ending Balance at Dec. 31, 2019	$ 40	$ 529,658	$ (282,197)	$ (158)	$ 247,343
Ending Balance, Shares at Dec. 31, 2019	39,655