CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2015		34,733,117
Beginning balance at Dec. 31, 2015	$ 932,264	$ 347	$ 1,233,786	$ (4,205)	$ (297,664)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock purchase plan (in shares)		79,324
Issuance of common stock under employee stock purchase plan	1,468	$ 1	1,467
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		355,450
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	230	$ 3	227
Repurchase of common stock pursuant to the 2016 share repurchase program (in shares)		(831,744)
Repurchase of common stock pursuant to the 2016 share repurchase program	(20,000)	$ (8)	(19,992)
Non-cash equity-based compensation	22,543		22,543
Unrealized losses on securities, net of tax	367			367
Net loss	(2,483)				(2,483)
Ending balance (in shares) at Dec. 31, 2016		34,336,147
Ending balance at Dec. 31, 2016	934,389	$ 343	1,238,031	(3,838)	(300,147)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of warrants	323		323
Equity component of the 2022 Convertible Notes, net of issuance costs and taxes	43,236		43,236
Equity component of debt repurchase	(27,988)		(27,988)
Shares issued in connection with Endoceutics License Agreement (in shares)		600,000
Shares issued in connection with Endoceutics License Agreement	$ 13,500	$ 6	13,494
Repurchase and retirement of common stock pursuant to the 2016 Share Repurchase Program (in shares)	(1,366,266)	(1,366,266)
Repurchase and retirement of common stock pursuant to the 2016 Share Repurchase Program	$ (19,467)	$ (14)	(19,453)
Issuance of common stock under employee stock purchase plan (in shares)		120,580
Issuance of common stock under employee stock purchase plan	1,594	$ 1	1,593
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		392,651
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(1,267)	$ 5	(1,272)
Non-cash equity-based compensation	23,664		23,664
Unrealized losses on securities, net of tax	(70)			(70)
Net loss	$ (199,228)				(199,228)
Ending balance (in shares) at Dec. 31, 2017	34,083,112	34,083,112
Ending balance at Dec. 31, 2017	$ 790,244	$ 341	1,271,628	(3,908)	(477,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock purchase plan (in shares)		59,872
Issuance of common stock under employee stock purchase plan	918	$ 1	917
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		463,776
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	279	$ 4	275
Non-cash equity-based compensation	19,916		19,916
Unrealized losses on securities, net of tax	(77)			(77)
Net loss	$ (65,761)				(65,761)
Ending balance (in shares) at Dec. 31, 2018	34,606,760	34,606,760
Ending balance at Dec. 31, 2018	$ 746,655	$ 346	$ 1,292,736	$ (3,985)	$ (542,442)