Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	IPO	Common Stock	Common Stock IPO	Additional Paid-In Capital	Additional Paid-In Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Loss	Non-controlling Interest (SRX Cardio)
Balance at beginning of year at Dec. 31, 2015	$ 430,323		$ 57		$ 1,076,791		$ (649,302)	$ (150)	$ 2,927
Balance at beginning of year (in shares) at Dec. 31, 2015			56,359,515
Exercise of employee stock options for cash	401				401
Exercise of employee stock options for cash (in shares)			54,045
Issuance of common stock pursuant to ESPP purchase	1,278				1,278
Issuance of common stock pursuant to ESPP purchase (in shares)			62,293
Issuance of common stock pursuant to RSU and PSU release (in shares)			68,365
Stock-based compensation expense	30,362				30,362
Unrealized gain (loss) on available-for-sale securities	138							138
Net (loss) income attributable to non-controlling interest (SRX Cardio)	930								930
Dividends to non-controlling interest (SRX Cardio)'s shareholders	(1,700)								(1,700)
Net loss	(269,043)						(269,043)
Balance at end of the year at Dec. 31, 2016	192,689		$ 57		1,108,832		(918,345)	(12)	2,157
Balance at end of the year (in shares) at Dec. 31, 2016			56,544,218
Cumulative effect of a change in accounting principal					84		(84)
Exercise of employee stock options for cash	17,697		$ 1		17,696
Exercise of employee stock options for cash (in shares)			1,092,539
Issuance of common stock pursuant to ESPP purchase	1,945				1,945
Issuance of common stock pursuant to ESPP purchase (in shares)			85,170
Issuance of common stock pursuant to RSU and PSU release	1		$ 1
Issuance of common stock pursuant to RSU and PSU release (in shares)			272,256
Stock-based compensation expense	43,284				43,284
Unrealized gain (loss) on available-for-sale securities	(397)							(397)
Net (loss) income attributable to non-controlling interest (SRX Cardio)	470								470
Issuance of common stock in connection with public offering, net		$ 379,894		$ 7		$ 379,887
Issuance of stock (in shares)				7,302,500
Net loss	(286,090)						(286,090)
Balance at end of the year at Dec. 31, 2017	349,493		$ 66		1,551,728		(1,204,519)	(409)	2,627
Balance at end of the year (in shares) at Dec. 31, 2017			65,296,683
Adjustment to accumulated deficit due to adoption of ASC 606	29,038						29,038
Exercise of employee stock options for cash	12,255		$ 1		12,254
Exercise of employee stock options for cash (in shares)			717,422
Issuance of common stock pursuant to ESPP purchase	3,133				3,133
Issuance of common stock pursuant to ESPP purchase (in shares)			105,997
Issuance of common stock pursuant to RSU and PSU release	1		$ 1
Issuance of common stock pursuant to RSU and PSU release (in shares)			497,662
Stock-based compensation expense	47,205				47,205
Unrealized gain (loss) on available-for-sale securities	126							126
Net (loss) income attributable to non-controlling interest (SRX Cardio)	(321)								(321)
Dividends to non-controlling interest (SRX Cardio)'s shareholders	(140)								(140)
Net loss	(350,223)						(350,223)
Balance at end of the year at Dec. 31, 2018	$ 90,567		$ 68		$ 1,614,320		$ (1,525,704)	$ (283)	$ 2,166
Balance at end of the year (in shares) at Dec. 31, 2018			66,617,764